Fuzz: exercise the selected region in FormatOutOfCountryCallingNumber, cap manual duration

[twcclegg]

Changes

Two coverage/UX gaps from the aggressive v9.0.37..main re-review — not correctness bugs in the shipped library (PhoneNumbers.Fuzz isn't part of the packed NuGet package).

• csharp/PhoneNumbers.Fuzz/Program.cs: FormatOutOfCountryCallingNumber was always fuzzed with a hardcoded "US" calling region, so formatting-from-region-specific branches (a region sharing the parsed number's country code, or with unusual national-prefix/IDD rules) got zero coverage regardless of how long the fuzzer ran. It now reuses the same fuzzer-selected region already threaded through Parse/FindNumbers/FormatAsYouType.
• .github/workflows/fuzz.yml: the workflow_dispatch duration input (seconds) had no upper bound against the job's 60-minute timeout-minutes. An oversized manual value doesn't make libFuzzer stop later — it makes the runner hard-cancel the whole job instead, which skips the "Upload crashes" step (if: failure() doesn't fire on a cancellation) and loses whatever crash was found. Capped to 3000s (50 min) via min(fromJSON(...), 3000), leaving headroom for checkout/build/instrument/upload within the 60-minute budget.

Test plan

• dotnet build csharp/PhoneNumbers.Fuzz -c Release — clean, 0 warnings.
• Ran the harness in reproduce mode against all 9 checked-in corpus files — all pass.
• Ran it against a synthetic input with 8 different region-selector byte values (0, 1, 50, 100, 150, 200, 250, 255) covering a spread of regions through FormatOutOfCountryCallingNumber — all format without throwing.
• YAML-parsed the workflow file.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 87.26%. Comparing base (25d7aaf) to head (9dba092).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #429   +/-   ##
=======================================
  Coverage   87.26%   87.26%           
=======================================
  Files          41       41           
  Lines        3831     3831           
  Branches      978      978           
=======================================
  Hits         3343     3343           
  Misses        284      284           
  Partials      204      204           

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