perf: Do not allocate for scope attributes that collide with reserved ones

[ArthurSens]

Follow up from #3503 (comment)

Changes

Prevent allocation in format! for labels that we know will collide with reserved ones.

Merge requirement checklist

• CONTRIBUTING guidelines followed
• Unit tests added/updated (if applicable)
• Appropriate CHANGELOG.md files updated for non-trivial, user-facing changes
• Changes in public API reviewed (if applicable)

[ArthurSens]

I considered removing this, but if we get something like schema-url, it will become schema_url after sanitization, and we need to drop it as well.

Is there a way that we can avoid allocation when they match a regex? I assume not, since regex is usually more resource-intensive than an exact match...?

[cijothomas]

agreed. this PR is good as-is.

[codecov]

Codecov Report

❌ Patch coverage is 0% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 82.8%. Comparing base (874633d) to head (6c5460e).

Files with missing lines	Patch %	Lines
opentelemetry-prometheus/src/lib.rs	0.0%	3 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##            main   #3548     +/-   ##
=======================================
- Coverage   82.8%   82.8%   -0.1%     
=======================================
  Files        130     130             
  Lines      27353   27356      +3     
=======================================
  Hits       22675   22675             
- Misses      4678    4681      +3     

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