Revert "Switch percentiles implementation to MergingDigest (#18124)"

[peteralfonsi]

Description

Reverts #18124.

As discussed with @msfroh in #18476, we are seeing some worrying AssertionErrors coming out of MergingDigest.quantile() in flaky tests. While that assertion error in particular is probably just due to tdunning/t-digest#167 and doesn't suggest broader issues with correctness, we're concerned there might be other lurking bugs in the MergingDigest implementation. So, we are reverting to the older AVLTreeDigest. Since there haven't been any major version releases since the original PR was merged, there shouldn't be any BWC issues.

I'll also reach out to the library creator and see if we can get some more info on this issue. If there's time I'll investigate the Apache implementation of MergingDigest as well.

Related Issues

Resolves #18476

Check List

• Functionality includes testing.
• [N/A] API changes companion pull request created, if applicable.
• [N/A] Public documentation issue/PR created, if applicable.

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[github-actions]

❌ Gradle check result for 13c2261: FAILURE

Please examine the workflow log, locate, and copy-paste the failure(s) below, then iterate to green. Is the failure a flaky test unrelated to your change?

[peteralfonsi]

Flaky test: #14309

[peteralfonsi]

Flaky test: #14324

[github-actions]

❌ Gradle check result for 0ebe747: FAILURE

Please examine the workflow log, locate, and copy-paste the failure(s) below, then iterate to green. Is the failure a flaky test unrelated to your change?

[peteralfonsi]

#14559

[github-actions]

❌ Gradle check result for ac009e8: FAILURE

Please examine the workflow log, locate, and copy-paste the failure(s) below, then iterate to green. Is the failure a flaky test unrelated to your change?

[peteralfonsi]

Flaky test: #17154

[github-actions]

✅ Gradle check result for 167102d: SUCCESS

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 72.69%. Comparing base (5255f5b) to head (167102d).
Report is 9 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff              @@
##               main   #18497      +/-   ##
============================================
- Coverage     72.71%   72.69%   -0.02%     
- Complexity    68094    68127      +33     
============================================
  Files          5537     5537              
  Lines        313312   313352      +40     
  Branches      45460    45469       +9     
============================================
- Hits         227813   227784      -29     
- Misses        66967    67082     +115     
+ Partials      18532    18486      -46     

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[peteralfonsi]

@msfroh or @andrross - finally got a green build on this, should be ready to merge

[msfroh]

Thanks @peteralfonsi!

[andrross]

@msfroh @peteralfonsi Let's make sure this revert gets into the 3.1 branch so that we revert this from the 3.1 release