Vector agg: skip entire null words of filter bitmap

[akuzm]

This improves the performance for highly selective filters.

[codecov]

Codecov Report

Attention: Patch coverage is 87.50000% with 3 lines in your changes missing coverage. Please review.

Project coverage is 82.31%. Comparing base (59f50f2) to head (9b47614).
Report is 688 commits behind head on main.

Files with missing lines	Patch %	Lines
tsl/src/nodes/vector_agg/grouping_policy_hash.c	86.95%	0 Missing and 3 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #7569      +/-   ##
==========================================
+ Coverage   80.06%   82.31%   +2.24%     
==========================================
  Files         190      238      +48     
  Lines       37181    43743    +6562     
  Branches     9450    10978    +1528     
==========================================
+ Hits        29770    36005    +6235     
- Misses       2997     3400     +403     
+ Partials     4414     4338      -76     

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[akuzm]

I'll remove it from the 2.18 milestone, because I want to check more things and this optimization is not strictly necessary.