perf(sdk-trace-base): optimize Span.{addEvent,addLink} performance

[daniellockyer]

Which problem is this PR solving?

Improves the performance of Span.{addEvent,addLink} by applying the same changes as b97b488 (by @AbhiPrasad) and #6514 (by me)

Before:

addEvent (128 attributes) x 9,581 ops/sec ±0.47% (99 runs sampled)
addLink (128 attributes) x 9,481 ops/sec ±0.14% (101 runs sampled)

After:

addEvent (128 attributes) x 76,473 ops/sec ±0.63% (95 runs sampled)
addLink (128 attributes) x 76,953 ops/sec ±0.11% (102 runs sampled)

refs #6100

Short description of the changes

• Remove use of Object.entries, as this is not performant as a for-in loop
• Remove use of Object.keys(..).length in a loop and use a variable to track count
• Add new benchmarks for these changes.

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

How Has This Been Tested?

Tests still pass, and you can see benchmarks above

Checklist:

• Followed the style guidelines of this project
• Unit tests have been added
• Documentation has been updated

[AbhiPrasad]

nice!

[codecov]

Codecov Report

❌ Patch coverage is 86.66667% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 95.73%. Comparing base (e9831e7) to head (ae7f691).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
packages/opentelemetry-sdk-trace-base/src/Span.ts	86.66%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6516      +/-   ##
==========================================
- Coverage   95.75%   95.73%   -0.02%     
==========================================
  Files         364      364              
  Lines       12096    12104       +8     
  Branches     2885     2887       +2     
==========================================
+ Hits        11582    11588       +6     
- Misses        514      516       +2     

Files with missing lines	Coverage Δ
packages/opentelemetry-sdk-trace-base/src/Span.ts	98.31% <86.66%> (-0.82%)	⬇️

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[daniellockyer]

Fixed my conflicts from main 🙂

[otelbot]

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