Add extract_if

[MitchellBerend]

This pr adds the extract_if method on the DefaultBTreeMap. This also bumps
the msrv from 1.88 to 1.91.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 96.39%. Comparing base (cf9f041) to head (4b18971).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #29      +/-   ##
==========================================
+ Coverage   96.30%   96.39%   +0.08%     
==========================================
  Files           2        2              
  Lines         298      305       +7     
==========================================
+ Hits          287      294       +7     
  Misses         11       11              

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