perf: Avoid unnecessary rechunk when sorting already sorted DataFrame

[gab23r]

Fixes #25733
Removed unconditional rechunk_mut_par() call from the sort executor.
sort_impl already handles rechunking after checking if a fast path (already sorted) can be taken, so the executor's rechunk was redundant

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 81.57%. Comparing base (86f9210) to head (4914e71).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #27264   +/-   ##
=======================================
  Coverage   81.56%   81.57%           
=======================================
  Files        1820     1820           
  Lines      251061   251060    -1     
  Branches     3149     3149           
=======================================
+ Hits       204788   204796    +8     
+ Misses      45465    45456    -9     
  Partials      808      808           

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