Apply per-endpoint limits to active requests

[bojbrook]

What does this PR do?

This PR introduces per-endpoint active request limits instead of a single global limit.

This ensures that slow or high-latency endpoints cannot monopolize the active requests, preventing unrelated endpoints from having their payloads dropped under load.

Motivation

Working with @BridgeAR on issue APMS-16671 where the customer was hitting the max requests limit of the tracer

Plugin Checklist

• Unit tests.
• Integration tests.
• Benchmarks.
• TypeScript definitions.
• TypeScript tests.
• API documentation.
• CI jobs/workflows.

Additional Notes

[github-actions]

Overall package size

Self size: 4.39 MB
Deduped: 5.22 MB
No deduping: 5.22 MB

Dependency sizes

| name | version | self size | total size | |------|---------|-----------|------------| | import-in-the-middle | 2.0.0 | 68.46 kB | 797.03 kB | | dc-polyfill | 0.1.10 | 26.73 kB | 26.73 kB |

_{🤖 This report was automatically generated by heaviest-objects-in-the-universe}

[codecov]

Codecov Report

❌ Patch coverage is 89.68254% with 13 lines in your changes missing coverage. Please review.
✅ Project coverage is 84.72%. Comparing base (033993d) to head (c236522).

Files with missing lines	Patch %	Lines
packages/dd-trace/src/exporters/common/request.js	93.91%	7 Missing ⚠️
packages/dd-trace/src/exporters/common/writer.js	50.00%	3 Missing ⚠️
packages/dd-trace/src/exporters/agent/writer.js	33.33%	2 Missing ⚠️
packages/dd-trace/src/datastreams/writer.js	50.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #7259      +/-   ##
==========================================
- Coverage   85.13%   84.72%   -0.41%     
==========================================
  Files         532      523       -9     
  Lines       22654    22544     -110     
==========================================
- Hits        19287    19101     -186     
- Misses       3367     3443      +76     

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