fix: can't filter on string column which has FTS index

[BubbleCal]

also fix BTree index isn't used if the column is with LargeUtf8 data type

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 48.48485% with 34 lines in your changes missing coverage. Please review.

Project coverage is 77.86%. Comparing base (ce1e61c) to head (ad3ee08).

Files with missing lines	Patch %	Lines
rust/lance/src/dataset/scanner.rs	0.00%	13 Missing ⚠️
rust/lance/src/index/scalar.rs	60.86%	6 Missing and 3 partials ⚠️
rust/lance/src/index.rs	69.23%	0 Missing and 8 partials ⚠️
rust/lance-datafusion/src/expr.rs	0.00%	4 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2875   +/-   ##
=======================================
  Coverage   77.85%   77.86%           
=======================================
  Files         231      231           
  Lines       70382    70413   +31     
  Branches    70382    70413   +31     
=======================================
+ Hits        54799    54826   +27     
- Misses      12458    12459    +1     
- Partials     3125     3128    +3     

Flag	Coverage Δ
unittests	77.86% <48.48%> (+<0.01%)	⬆️

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[westonpace]

Nicely done, thanks!