fix: Optimize memory on rolling groups in ApplyExpr

[kdn36]

fixes #22725

This PR introduces a lazy iterator over groups iter_groups_lazy(), which helps to avoid memory explosion when groups are overlapping (rolling).

The initial PR has the minimum code to fix the issue reported above. More work is needed: (i) add GroupsType::Idx implementation, (ii) provide an indexed parallel iterator for multi-threading , (iii) leverage the iterators in other expressions and/or implementation paths that may suffer from the same memory explosion pattern when aggregating from NotAggregated to AggregatedList on rolling groups.

Micro-benchmark results (/usr/bin/time -v on debug build on the MRE as documented in the issue, single-threaded).
Memory reduced from 1.6 GB to 132 MB.

• Before: Maximum resident set size (kbytes): 1734688
• After: Maximum resident set size (kbytes): 131732

For the original issue: from 11.8 GB to 0.36 GB.

Ping @coastalwhite

[codecov]

Codecov Report

❌ Patch coverage is 94.87179% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 81.80%. Comparing base (7173122) to head (ecc517d).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
crates/polars-expr/src/expressions/group_iter.rs	94.82%	3 Missing ⚠️
crates/polars-expr/src/expressions/apply.rs	95.00%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #24709   +/-   ##
=======================================
  Coverage   81.79%   81.80%           
=======================================
  Files        1704     1704           
  Lines      235223   235290   +67     
  Branches     2997     2997           
=======================================
+ Hits       192410   192479   +69     
+ Misses      42048    42046    -2     
  Partials      765      765           

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