feat: Add getter for pre-batch buffer sizes

[fredjoonpark]

Proposed Changes

This PR adds a getter for fetching pre-batch buffer sizes. Adds an opt-in flag enableBufferTracking which can be disabled for consumers that do not need this feature.

Checklist

• CHANGELOG.md updated
• Rebased/mergeable
• A test has been added if appropriate
• mvn test completes successfully
• Commit messages are conventional
• Sign CLA (if not already signed)

[codecov-commenter]

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Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 88.90%. Comparing base (6662d8c) to head (efe39e6).
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Additional details and impacted files

@@             Coverage Diff              @@
##             master     #857      +/-   ##
============================================
+ Coverage     88.81%   88.90%   +0.09%     
  Complexity      791      791              
============================================
  Files           174      174              
  Lines          7250     7291      +41     
  Branches        413      415       +2     
============================================
+ Hits           6439     6482      +43     
+ Misses          680      679       -1     
+ Partials        131      130       -1     

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