Fix delta aggregation metric reuse

[jtescher]

Fixes #1432

Changes

This simplifies data aggregation by clearing data points instead of the current more complicated re-use strategy.

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)

[codecov]

Codecov Report

Attention: 9 lines in your changes are missing coverage. Please review.

Comparison is base (bd3ba65) 58.3% compared to head (0fb099b) 60.4%.
Report is 1 commits behind head on main.

❗ Current head 0fb099b differs from pull request most recent head d2b9a9f. Consider uploading reports for the commit d2b9a9f to get more accurate results

Files	Patch %	Lines
...-sdk/src/metrics/internal/exponential_histogram.rs	92.5%	4 Missing ⚠️
opentelemetry-sdk/src/metrics/internal/sum.rs	93.1%	3 Missing ⚠️
...entelemetry-sdk/src/metrics/internal/last_value.rs	81.8%	2 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##            main   #1434     +/-   ##
=======================================
+ Coverage   58.3%   60.4%   +2.0%     
=======================================
  Files        146     146             
  Lines      18827   18807     -20     
=======================================
+ Hits       10994   11360    +366     
+ Misses      7833    7447    -386     

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[hdost]

Thank you for the fix!