fix: sort partition, track size

[dkharms]

Description

We had several flaky tests:

• TestOldestMetrics;
• TestCapacityExceeded;
• TestFracInfoCache

They were flaky because we dropped the whole partition even if we drop more than necessary. And we dropped fractions of partition in random order hence.

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[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 71.28%. Comparing base (3a58354) to head (c9bfea3).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #536      +/-   ##
==========================================
+ Coverage   71.27%   71.28%   +0.01%     
==========================================
  Files         250      250              
  Lines       21783    21785       +2     
==========================================
+ Hits        15526    15530       +4     
+ Misses       5099     5098       -1     
+ Partials     1158     1157       -1     

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