refactor(rust): Add groupby partitioning and parallel groupby finishing to new-streaming engine

[orlp]

No description provided.

[codecov]

Codecov Report

Attention: Patch coverage is 1.10497% with 358 lines in your changes missing coverage. Please review.

Project coverage is 79.81%. Comparing base (1452468) to head (21ad2b7).
Report is 95 commits behind head on main.

Files with missing lines	Patch %	Lines
crates/polars-arrow/src/bitmap/builder.rs	0.00%	66 Missing ⚠️
crates/polars-expr/src/reduce/partition.rs	0.00%	65 Missing ⚠️
crates/polars-stream/src/nodes/group_by.rs	0.00%	65 Missing ⚠️
crates/polars-expr/src/groups/row_encoded.rs	0.00%	63 Missing ⚠️
crates/polars-expr/src/reduce/mod.rs	0.00%	38 Missing ⚠️
crates/polars-expr/src/reduce/min_max.rs	0.00%	36 Missing ⚠️
crates/polars-expr/src/reduce/sum.rs	0.00%	15 Missing ⚠️
crates/polars-expr/src/reduce/len.rs	0.00%	10 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #19451      +/-   ##
==========================================
- Coverage   79.97%   79.81%   -0.17%     
==========================================
  Files        1533     1536       +3     
  Lines      210916   211401     +485     
  Branches     2442     2444       +2     
==========================================
+ Hits       168688   168732      +44     
- Misses      41673    42114     +441     
  Partials      555      555              

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