perf(sdk-trace-base): use counter for attribute limit check in Span

[AbhiPrasad]

Which problem is this PR solving?

Replace O(n) Object.keys().length call with O(1) counter lookup when checking attribute count limits in setAttribute().

Benchmark results show up to 22x improvement for spans with 128 attributes (worst case). From my experience at Sentry, most auto-instrumented Node.js spans tend to have ~50-60 attributes, so I'd expect atleast a 5x speedup in the average case.

Short description of the changes

• Added _attributesCount private counter field to SpanImpl class to track the number of attributes
• Replaced Object.keys(this.attributes).length (O(n)) with this._attributesCount (O(1)) in the attribute limit check
• Counter is only incremented when adding a new key, not when overwriting an existing one

Type of change

Performance improvement

How Has This Been Tested?

Add a new benchmark for this (AI generated). Tested on a 2021 Apple M1 Pro 32 GB - MacOS 15.5 (24F74)

Scenario	Before	After	Improvement
10 attributes	891,847 ops/sec	945,411 ops/sec	1.06x
50 attributes	66,547 ops/sec	312,021 ops/sec	4.7x
100 attributes	13,409 ops/sec	172,770 ops/sec	12.9x
128 attributes	6,599 ops/sec	147,883 ops/sec	22.4x
setAttributes bulk (100)	11,403 ops/sec	51,676 ops/sec	4.5x

Checklist:

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

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 95.68%. Comparing base (903739c) to head (ff7c343).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #6283   +/-   ##
=======================================
  Coverage   95.68%   95.68%           
=======================================
  Files         313      313           
  Lines        9667     9671    +4     
  Branches     2226     2227    +1     
=======================================
+ Hits         9250     9254    +4     
  Misses        417      417           

Files with missing lines	Coverage Δ
packages/opentelemetry-sdk-trace-base/src/Span.ts	97.75% <100.00%> (+0.05%)	⬆️

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[david-luna]

@AbhiPrasad this PR has some conflicts. Could you please update? Thank you!

[AbhiPrasad]

I think the unit test failure is a flake

> opentelemetry@0.1.0 precompile
> npm run submodule && nx run-many -t protos:generate && nx run-many -t version


> opentelemetry@0.1.0 submodule
> git submodule sync --recursive && git submodule update --init --recursive

Submodule 'experimental/packages/otlp-transformer/protos' (https://github.com/open-telemetry/opentelemetry-proto.git) registered for path 'experimental/packages/otlp-transformer/protos'
Cloning into '/home/runner/work/opentelemetry-js/opentelemetry-js/experimental/packages/otlp-transformer/protos'...
Submodule path 'experimental/packages/otlp-transformer/protos': checked out '8654ab7a5a43ca25fe8046e59dcd6935c3f76de0'
Segmentation fault (core dumped)
Error: Process completed with exit code 139.

[david-luna]

Restarted the check. Let see if it goes through