fix: Refactor BinaryExpr in group_by with partial sort

[kdn36]

fixes #24504
fixed undocumented issues (e.g. mismatching groups similar to #24500 but for BinaryExpr)

This PR is a refactor similar to #24520 but for BinaryExpr instead of ApplyExpr. It includes regression tests for all combinations of aggstates, with and without partial sort, as well as raising an error on groups mismatch.

Not to be merged until:
(i) The PR for the reference case of ApplyExpr has been approved for merged; and this PR is rebased on it.
(ii) TODO: scope decision on how to handle dynamic_group_by, preferably by evolving the concept of rolling to overlapping.
(iii) TODO: consolidate dispatch logic.
(iv) Performance regression check.

[codecov]

Codecov Report

❌ Patch coverage is 98.61111% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 81.75%. Comparing base (f0fc158) to head (9c1aa3a).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
crates/polars-expr/src/expressions/binary.rs	98.33%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #24548      +/-   ##
==========================================
- Coverage   81.81%   81.75%   -0.07%     
==========================================
  Files        1683     1684       +1     
  Lines      229051   229509     +458     
  Branches     2946     2952       +6     
==========================================
+ Hits       187406   187641     +235     
- Misses      40906    41125     +219     
- Partials      739      743       +4     

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