Strip the national prefix without materialising a match

[twcclegg]

ParseNationalFormat still carries ~215 B over a plain E164 parse, and that residue is the Match
object itself — #384 removed the group accesses around it but the match remained.

Whether the groups are needed is knowable before matching: only a transform rule or a requested
carrier code reads them, and after #384 a plain Parse requests neither. Without them, the only
thing this method uses is the prefix length.

So there is now a fast path that never materialises a Match:

• Literal prefixes — the metadata already caches whether the pattern is a literal, and a literal
  matches itself, so the length is known without running a regex at all. Many regions are plain 0.
• Everything else on net7.0+ — Regex.EnumerateMatches yields a ValueMatch struct with
  Index/Length and allocates nothing.
• netstandard2.0 — unchanged, falls back to MatchBeginning.

The slow path is untouched, so a transform rule or a carrier request behaves exactly as before, and
the public MaybeStripNationalPrefixAndCarrierCode overload still passes carrierCode != null.

Watch ParseNationalFormat; ParseOnly and ParseWithExtension should not move.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.01%. Comparing base (bce4b27) to head (d17b638).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #385      +/-   ##
==========================================
- Coverage   98.01%   98.01%   -0.01%     
==========================================
  Files          39       39              
  Lines       52822    52842      +20     
  Branches     1106     1115       +9     
==========================================
+ Hits        51774    51793      +19     
  Misses        795      795              
- Partials      253      254       +1     

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[github-actions]

📊 Benchmark Results

Commit: d17b638 · Full run · Linux ubuntu-24.04-arm

Both sides were measured on the same runner in the same job, so the numbers are
comparable. Treat sub-percent differences as noise.

PR branch

BenchmarkDotNet v0.15.8, Linux Ubuntu 24.04.4 LTS (Noble Numbat)
Neoverse-N2, 4 physical cores
.NET SDK 10.0.302
  [Host]    : .NET 10.0.10 (10.0.10, 10.0.1026.32716), Arm64 RyuJIT armv8.0-a
  .NET 10.0 : .NET 10.0.10 (10.0.10, 10.0.1026.32716), Arm64 RyuJIT armv8.0-a

Job=.NET 10.0  Runtime=.NET 10.0  

Method	PhoneNumberCount	Mean	Error	StdDev	Gen0	Allocated
InputDigitPerKeystroke	1000	4.262 ms	0.0148 ms	0.0138 ms	54.6875	3.87 MB

BenchmarkDotNet v0.15.8, Linux Ubuntu 24.04.4 LTS (Noble Numbat)
Neoverse-N2, 4 physical cores
.NET SDK 10.0.302
  [Host]     : .NET 10.0.10 (10.0.10, 10.0.1026.32716), Arm64 RyuJIT armv8.0-a
  Job-AMQORM : .NET 10.0.10 (10.0.10, 10.0.1026.32716), Arm64 RyuJIT armv8.0-a

Runtime=.NET 10.0  InvocationCount=1  IterationCount=20  
LaunchCount=1  RunStrategy=ColdStart  UnrollFactor=1  
WarmupCount=1  

Method	Mean	Error	StdDev	Allocated
CreateInstance	401.2 μs	103.0 μs	118.7 μs	119.48 KB
CreateInstanceAndLoadAllRegions	7,021.4 μs	393.0 μs	452.6 μs	1619.1 KB
FirstRegionLookup	452.9 μs	143.3 μs	165.0 μs	124.54 KB

BenchmarkDotNet v0.15.8, Linux Ubuntu 24.04.4 LTS (Noble Numbat)
Neoverse-N2, 4 physical cores
.NET SDK 10.0.302
  [Host]    : .NET 10.0.10 (10.0.10, 10.0.1026.32716), Arm64 RyuJIT armv8.0-a
  .NET 10.0 : .NET 10.0.10 (10.0.10, 10.0.1026.32716), Arm64 RyuJIT armv8.0-a

Job=.NET 10.0  Runtime=.NET 10.0  

Method	PhoneNumberCount	Mean	Error	StdDev	Gen0	Allocated
ExtractPossibleNumber_CleanInput	1000	21.54 μs	0.012 μs	0.010 μs	-	-
ExtractPossibleNumber_WithLeadingJunk	1000	38.07 μs	0.048 μs	0.042 μs	0.6714	48360 B

BenchmarkDotNet v0.15.8, Linux Ubuntu 24.04.4 LTS (Noble Numbat)
Neoverse-N2, 4 physical cores
.NET SDK 10.0.302
  [Host]    : .NET 10.0.10 (10.0.10, 10.0.1026.32716), Arm64 RyuJIT armv8.0-a
  .NET 10.0 : .NET 10.0.10 (10.0.10, 10.0.1026.32716), Arm64 RyuJIT armv8.0-a

Job=.NET 10.0  Runtime=.NET 10.0  

Method	PhoneNumberCount	Mean	Error	StdDev	Gen0	Allocated
FindNumbers_Valid	100	142.0 μs	1.01 μs	0.95 μs	0.9766	70.71 KB
FindNumbers_StrictGrouping	100	308.1 μs	0.69 μs	0.64 μs	1.4648	123.99 KB

BenchmarkDotNet v0.15.8, Linux Ubuntu 24.04.4 LTS (Noble Numbat)
Neoverse-N2, 4 physical cores
.NET SDK 10.0.302
  [Host]    : .NET 10.0.10 (10.0.10, 10.0.1026.32716), Arm64 RyuJIT armv8.0-a
  .NET 10.0 : .NET 10.0.10 (10.0.10, 10.0.1026.32716), Arm64 RyuJIT armv8.0-a

Job=.NET 10.0  Runtime=.NET 10.0  

Method	PhoneNumberCount	Mean	Error	StdDev	Gen0	Allocated
GetDescriptionForNumber	1000	1,383.85 μs	4.316 μs	4.037 μs	1.9531	196.63 KB
GetDisplayCountry	1000	43.77 μs	0.112 μs	0.099 μs	0.0610	7.56 KB

BenchmarkDotNet v0.15.8, Linux Ubuntu 24.04.4 LTS (Noble Numbat)
Neoverse-N2, 4 physical cores
.NET SDK 10.0.302
  [Host]    : .NET 10.0.10 (10.0.10, 10.0.1026.32716), Arm64 RyuJIT armv8.0-a
  .NET 10.0 : .NET 10.0.10 (10.0.10, 10.0.1026.32716), Arm64 RyuJIT armv8.0-a

Job=.NET 10.0  Runtime=.NET 10.0  

Method	PhoneNumberCount	Mean	Error	StdDev	Median	Gen0	Allocated
ParseValidateAndFormatPhoneNumbers	1000	2,493.2 μs	48.27 μs	67.67 μs	2,455.2 μs	7.8125	577.71 KB
ParseOnly	1000	433.5 μs	0.63 μs	0.59 μs	433.3 μs	4.8828	348.13 KB
ParseNationalFormat	1000	782.7 μs	1.34 μs	1.19 μs	782.5 μs	6.8359	487.04 KB
ParseWithExtension	1000	1,110.6 μs	2.08 μs	1.95 μs	1,110.0 μs	13.6719	957.38 KB
ValidateOnly	1000	699.1 μs	1.45 μs	1.28 μs	699.4 μs	-	41.11 KB
FormatOnly	1000	1,102.2 μs	2.90 μs	2.27 μs	1,101.7 μs	1.9531	187.92 KB

PR base

BenchmarkDotNet v0.15.8, Linux Ubuntu 24.04.4 LTS (Noble Numbat)
Neoverse-N2, 4 physical cores
.NET SDK 10.0.302
  [Host]    : .NET 10.0.10 (10.0.10, 10.0.1026.32716), Arm64 RyuJIT armv8.0-a
  .NET 10.0 : .NET 10.0.10 (10.0.10, 10.0.1026.32716), Arm64 RyuJIT armv8.0-a

Job=.NET 10.0  Runtime=.NET 10.0  

Method	PhoneNumberCount	Mean	Error	StdDev	Gen0	Allocated
InputDigitPerKeystroke	1000	4.261 ms	0.0100 ms	0.0084 ms	54.6875	3.87 MB

BenchmarkDotNet v0.15.8, Linux Ubuntu 24.04.4 LTS (Noble Numbat)
Neoverse-N2, 4 physical cores
.NET SDK 10.0.302
  [Host]     : .NET 10.0.10 (10.0.10, 10.0.1026.32716), Arm64 RyuJIT armv8.0-a
  Job-AMQORM : .NET 10.0.10 (10.0.10, 10.0.1026.32716), Arm64 RyuJIT armv8.0-a

Runtime=.NET 10.0  InvocationCount=1  IterationCount=20  
LaunchCount=1  RunStrategy=ColdStart  UnrollFactor=1  
WarmupCount=1  

Method	Mean	Error	StdDev	Allocated
CreateInstance	408.7 μs	114.0 μs	131.3 μs	119.48 KB
CreateInstanceAndLoadAllRegions	7,027.3 μs	444.8 μs	512.2 μs	1619.1 KB
FirstRegionLookup	464.7 μs	140.2 μs	161.4 μs	124.54 KB

BenchmarkDotNet v0.15.8, Linux Ubuntu 24.04.4 LTS (Noble Numbat)
Neoverse-N2, 4 physical cores
.NET SDK 10.0.302
  [Host]    : .NET 10.0.10 (10.0.10, 10.0.1026.32716), Arm64 RyuJIT armv8.0-a
  .NET 10.0 : .NET 10.0.10 (10.0.10, 10.0.1026.32716), Arm64 RyuJIT armv8.0-a

Job=.NET 10.0  Runtime=.NET 10.0  

Method	PhoneNumberCount	Mean	Error	StdDev	Gen0	Allocated
ExtractPossibleNumber_CleanInput	1000	20.89 μs	0.014 μs	0.013 μs	-	-
ExtractPossibleNumber_WithLeadingJunk	1000	37.30 μs	0.065 μs	0.054 μs	0.6714	48360 B

BenchmarkDotNet v0.15.8, Linux Ubuntu 24.04.4 LTS (Noble Numbat)
Neoverse-N2, 4 physical cores
.NET SDK 10.0.302
  [Host]    : .NET 10.0.10 (10.0.10, 10.0.1026.32716), Arm64 RyuJIT armv8.0-a
  .NET 10.0 : .NET 10.0.10 (10.0.10, 10.0.1026.32716), Arm64 RyuJIT armv8.0-a

Job=.NET 10.0  Runtime=.NET 10.0  

Method	PhoneNumberCount	Mean	Error	StdDev	Gen0	Allocated
FindNumbers_Valid	100	141.9 μs	0.25 μs	0.22 μs	0.9766	70.71 KB
FindNumbers_StrictGrouping	100	307.0 μs	2.20 μs	2.06 μs	1.4648	123.99 KB

BenchmarkDotNet v0.15.8, Linux Ubuntu 24.04.4 LTS (Noble Numbat)
Neoverse-N2, 4 physical cores
.NET SDK 10.0.302
  [Host]    : .NET 10.0.10 (10.0.10, 10.0.1026.32716), Arm64 RyuJIT armv8.0-a
  .NET 10.0 : .NET 10.0.10 (10.0.10, 10.0.1026.32716), Arm64 RyuJIT armv8.0-a

Job=.NET 10.0  Runtime=.NET 10.0  

Method	PhoneNumberCount	Mean	Error	StdDev	Gen0	Allocated
GetDescriptionForNumber	1000	1,460.12 μs	2.750 μs	2.296 μs	1.9531	196.63 KB
GetDisplayCountry	1000	24.52 μs	0.036 μs	0.034 μs	0.0916	7.56 KB

BenchmarkDotNet v0.15.8, Linux Ubuntu 24.04.4 LTS (Noble Numbat)
Neoverse-N2, 4 physical cores
.NET SDK 10.0.302
  [Host]    : .NET 10.0.10 (10.0.10, 10.0.1026.32716), Arm64 RyuJIT armv8.0-a
  .NET 10.0 : .NET 10.0.10 (10.0.10, 10.0.1026.32716), Arm64 RyuJIT armv8.0-a

Job=.NET 10.0  Runtime=.NET 10.0  

Method	PhoneNumberCount	Mean	Error	StdDev	Gen0	Allocated
ParseValidateAndFormatPhoneNumbers	1000	2,491.1 μs	3.58 μs	3.17 μs	7.8125	579.75 KB
ParseOnly	1000	439.5 μs	0.54 μs	0.45 μs	4.8828	350.16 KB
ParseNationalFormat	1000	842.2 μs	2.08 μs	1.94 μs	7.8125	564.95 KB
ParseWithExtension	1000	1,103.5 μs	7.73 μs	7.23 μs	13.6719	959.41 KB
ValidateOnly	1000	696.7 μs	5.92 μs	10.67 μs	-	41.11 KB
FormatOnly	1000	1,043.1 μs	2.23 μs	1.98 μs	1.9531	187.92 KB