Compile-time specializations for some hashing strategies

[akuzm]

Generate specialized code at compiled time for some vectorized grouping cases such as grouping by a single fixed-value column. This improves performance.

[codecov]

Codecov Report

Attention: Patch coverage is 54.54545% with 5 lines in your changes missing coverage. Please review.

Project coverage is 81.94%. Comparing base (9b2789d) to head (13bc063).

Files with missing lines	Patch %	Lines
.../src/nodes/vector_agg/hashing/hash_strategy_impl.c	54.54%	2 Missing and 3 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #8269      +/-   ##
==========================================
- Coverage   82.21%   81.94%   -0.28%     
==========================================
  Files         256      256              
  Lines       48184    48166      -18     
  Branches    12155    12154       -1     
==========================================
- Hits        39615    39468     -147     
- Misses       3704     3899     +195     
+ Partials     4865     4799      -66     

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