feat: add approx_count_rows method for efficient row counting with index selection

[Jay-ju]

No description provided.

[Jay-ju]

@jackye1995
This PR is based on #4735 and #4805 Regarding the discussion content, first provide an approximate line count and add some benchmark tests. It seems that the efficiency of the approximate calculation is still very high.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 72.64151% with 116 lines in your changes missing coverage. Please review.
✅ Project coverage is 81.73%. Comparing base (a3ed68d) to head (413cee1).
⚠️ Report is 3 commits behind head on main.

Files with missing lines	Patch %	Lines
rust/lance/src/dataset/fragment/approx.rs	71.42%	45 Missing and 7 partials ⚠️
rust/lance-index/src/scalar/expression.rs	77.77%	37 Missing and 3 partials ⚠️
rust/lance-index/src/scalar/zonemap.rs	32.14%	18 Missing and 1 partial ⚠️
rust/lance/src/dataset/scanner.rs	44.44%	4 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4930      +/-   ##
==========================================
+ Coverage   81.64%   81.73%   +0.08%     
==========================================
  Files         333      335       +2     
  Lines      131594   132843    +1249     
  Branches   131594   132843    +1249     
==========================================
+ Hits       107444   108581    +1137     
- Misses      20550    20613      +63     
- Partials     3600     3649      +49     

Flag	Coverage Δ
unittests	81.73% <72.64%> (+0.08%)	⬆️

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[Jay-ju]

@jackye1995 Please take a look at this PR when you have time.