refactor(instrumentation-http): refactor getIncomingRequestAttributes() to reduce work

[cjihrig]

Which problem is this PR solving?

getIncomingRequestAttributes() is on the stack 12% of the time in a flame graph I created for an HTTP server. Since this function is somewhat hot, it makes sense to optimize it a bit. More specifically, this function is computing two sets of attributes even though often only a single set of attributes is needed.

Fixes # N/A

Short description of the changes

This commit updates getIncomingRequestAttributes() to only compute the necessary attributes. On my local macOS machine running Node 25, this reduced the amount of time it was on the stack from 12% to 7%. The number of requests served also went from 372k to 390k (for more context, this was at 1350k requests for the same Node server without any OTel).

Type of change

None of these - performance refactor.

How Has This Been Tested?

• Test suite

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 95.40%. Comparing base (f9c995d) to head (43116f2).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #6207   +/-   ##
=======================================
  Coverage   95.40%   95.40%           
=======================================
  Files         317      317           
  Lines        9514     9514           
  Branches     2192     2192           
=======================================
  Hits         9077     9077           
  Misses        437      437           

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[cjihrig]

Maybe ping @maryliag who had originally asked me to look into potential perf improvements?

[maryliag]

Nice improvement! Thank you for working on this!

[otelbot]

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