refactor: Deprecate Expr.rechunk

[coastalwhite]

Fixes #22279.

[codecov]

Codecov Report

❌ Patch coverage is 75.00000% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 81.83%. Comparing base (39097fa) to head (1118afe).
⚠️ Report is 8 commits behind head on main.

Files with missing lines	Patch %	Lines
crates/polars-plan/src/dsl/function_expr/mod.rs	0.00%	1 Missing ⚠️
py-polars/src/polars/expr/expr.py	50.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #24772      +/-   ##
==========================================
- Coverage   81.85%   81.83%   -0.02%     
==========================================
  Files        1689     1691       +2     
  Lines      230819   230820       +1     
  Branches     2990     2992       +2     
==========================================
- Hits       188935   188890      -45     
- Misses      41124    41169      +45     
- Partials      760      761       +1     

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