feat: add IVF_HNSW_FLAT index

[BubbleCal]

No description provided.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 87.23404% with 6 lines in your changes missing coverage. Please review.

Project coverage is 78.69%. Comparing base (1afdf3f) to head (f62eb05).

Files with missing lines	Patch %	Lines
rust/lance/src/index/vector/ivf.rs	80.00%	0 Missing and 4 partials ⚠️
rust/lance-index/src/lib.rs	66.66%	1 Missing ⚠️
rust/lance/src/index.rs	90.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3671   +/-   ##
=======================================
  Coverage   78.68%   78.69%           
=======================================
  Files         285      285           
  Lines      113471   113516   +45     
  Branches   113471   113516   +45     
=======================================
+ Hits        89289    89326   +37     
- Misses      20758    20761    +3     
- Partials     3424     3429    +5     

Flag	Coverage Δ
unittests	78.69% <87.23%> (+<0.01%)	⬆️

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[SaintBacchus]

@BubbleCal I tested this pr and it works. Will you fix the CI issue and merge it into the next version?

[westonpace]

It's pretty cool that this was so easy to add. The abstractions you created are really paying off!