[SDK] Fix incorrect delta histogram scale after circular buffer reset

[matt-hensley]

Changes

Fixed CircularBufferBuckets reset handling so the internal state is cleared correctly.

Previously, stale state could cause an unnecessary scale reduction for the first recording in a new delta histogram.

Merge requirement checklist

• CONTRIBUTING guidelines followed (license requirements, nullable enabled, static analysis, etc.)
• Unit tests added/updated
• Appropriate CHANGELOG.md files updated for non-trivial changes
• Changes in public API reviewed (if applicable)

[opentelemetry-pr-dashboard]

Pull request dashboard status

Merged · refreshed 2026-09-17 06:23 UTC

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.86%. Comparing base (6265592) to head (b538ec9).
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #7749      +/-   ##
==========================================
- Coverage   91.87%   91.86%   -0.01%     
==========================================
  Files         337      337              
  Lines       18380    18382       +2     
==========================================
  Hits        16887    16887              
- Misses       1493     1495       +2     

Flag	Coverage Δ
unittests-Project-Experimental	91.94% <100.00%> (-0.05%)	⬇️
unittests-Project-Stable	91.95% <100.00%> (-0.05%)	⬇️

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Files with missing lines	Coverage Δ
src/OpenTelemetry/Metrics/CircularBufferBuckets.cs	100.00% <100.00%> (ø)

... and 5 files with indirect coverage changes