feat: update merge_insert to add statistics for inserted, updated, deleted rows

[raunaks13]

Addresses https://github.com/lancedb/lance/issues/2019

[github-actions[bot]]

ACTION NEEDED

Lance follows the Conventional Commits specification for release automation.

The PR title and description are used as the merge commit message. Please update your PR title and description to match the specification.

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[codecov-commenter]

Codecov Report

Attention: Patch coverage is 95.34884% with 4 lines in your changes are missing coverage. Please review.

Project coverage is 79.86%. Comparing base (7d9dbda) to head (721a15b). Report is 8 commits behind head on main.

Files	Patch %	Lines
rust/lance/src/dataset/write/merge_insert.rs	95.34%	1 Missing and 3 partials :warning:

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2357      +/-   ##
==========================================
- Coverage   80.69%   79.86%   -0.84%     
==========================================
  Files         192      191       -1     
  Lines       56193    53077    -3116     
  Branches    56193    53077    -3116     
==========================================
- Hits        45344    42389    -2955     
+ Misses       8221     8196      -25     
+ Partials     2628     2492     -136     

Flag	Coverage Δ
unittests	79.86% <95.34%> (-0.84%)	:arrow_down:

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