fix: ObservableCounter and ObservableUpDownCounter remove stale attribute combinations that are no longer observed

[taisho6339]

Fixes #3213

Changes

ObservableCounter and ObservableUpDownCounter now correctly report only data points from the current measurement cycle, removing stale attribute combinations that are no longer observed.

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)

[linux-foundation-easycla]

The committers listed above are authorized under a signed CLA.

• ✅ login: taisho6339 / name: Hiroki Sakamoto (b140f49)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 80.8%. Comparing base (95af815) to head (b140f49).

Additional details and impacted files

@@          Coverage Diff          @@
##            main   #3248   +/-   ##
=====================================
  Coverage   80.8%   80.8%           
=====================================
  Files        129     129           
  Lines      23199   23192    -7     
=====================================
- Hits       18745   18742    -3     
+ Misses      4454    4450    -4     

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