feat: Support decimal groupby

[flisky]

No description provided.

[codecov]

Codecov Report

Attention: Patch coverage is 58.33333% with 5 lines in your changes are missing coverage. Please review.

Project coverage is 80.99%. Comparing base (c5b53ab) to head (6961839).
Report is 6 commits behind head on main.

❗ Current head 6961839 differs from pull request most recent head 9b59c56. Consider uploading reports for the commit 9b59c56 to get more accurate results

Files	Patch %	Lines
crates/polars-utils/src/hashing.rs	0.00%	5 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #15000   +/-   ##
=======================================
  Coverage   80.98%   80.99%           
=======================================
  Files        1333     1333           
  Lines      173174   173186   +12     
  Branches     2458     2458           
=======================================
+ Hits       140252   140276   +24     
+ Misses      32454    32443   -11     
+ Partials      468      467    -1     

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[ritchie46]

Thank you @flisky. Looks good.