perf: change scalar index to return RowIdTreeMap instead of u64 array

[westonpace]

The filtering paths that use scalar indices are all built to use RowIdTreeMap. Scalar indices were built to use UInt64Array. This means we have to copy from one to the other (an O(N log(N)) operation. When we just had btree indices this was a fairly cheap operation since the indices shouldn't be returning large #'s of rows anyways. Now that we have BITMAP and LABEL_LIST we can have indices that return very large #'s of rows and this copy was expensive. By changing the scalar indices to use RowIdTreeMap directly we skip the conversion.

NOTE: any LABEL_LIST or BITMAP index that was previously created will be invalid and will need to be recreated. Since we haven't had an official release of these index types I am not considering this a breaking change.

[eddyxu]

LGTm

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 87.58621% with 18 lines in your changes missing coverage. Please review.

Project coverage is 79.91%. Comparing base (a237fca) to head (e0ef6a9).

Files	Patch %	Lines
rust/lance-core/src/utils/mask.rs	66.66%	6 Missing ⚠️
rust/lance-index/src/scalar/bitmap.rs	83.87%	5 Missing ⚠️
rust/lance-index/src/scalar/label_list.rs	85.18%	1 Missing and 3 partials ⚠️
rust/lance-index/src/scalar/lance_format.rs	95.74%	0 Missing and 2 partials ⚠️
rust/lance-index/src/scalar/flat.rs	83.33%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2587      +/-   ##
==========================================
- Coverage   79.93%   79.91%   -0.02%     
==========================================
  Files         212      212              
  Lines       61660    61639      -21     
  Branches    61660    61639      -21     
==========================================
- Hits        49285    49256      -29     
- Misses       9420     9445      +25     
+ Partials     2955     2938      -17     

Flag	Coverage Δ
unittests	79.91% <87.58%> (-0.02%)	⬇️

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