chore: update DataFusion to 50, Arrow to 56

[timsaucer]

Leaving as draft until datafusion-python 50.0.0 releases.

This is a dependency update for DataFusion and Arrow.

The only change that seems like it is impactful is that the arrow buffers no longer use a minimum capacity of 64 bytes. apache/arrow-rs#7984 appears to be the originating source. This updates the statistics that are generated in the unit test.

[timsaucer]

I'll rebase it before moving to ready. The first two commits are already in main.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 59.09091% with 9 lines in your changes missing coverage. Please review.
✅ Project coverage is 81.44%. Comparing base (c6eb6c0) to head (2171dea).

Files with missing lines	Patch %	Lines
rust/lance-datafusion/src/planner.rs	11.11%	7 Missing and 1 partial ⚠️
rust/lance/src/io/exec/optimizer.rs	83.33%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4778      +/-   ##
==========================================
+ Coverage   80.88%   81.44%   +0.55%     
==========================================
  Files         323      323              
  Lines      127646   125636    -2010     
  Branches   127646   125636    -2010     
==========================================
- Hits       103251   102319     -932     
+ Misses      20758    19888     -870     
+ Partials     3637     3429     -208     

Flag	Coverage Δ
unittests	81.44% <59.09%> (+0.55%)	⬆️

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[timsaucer]

Closing in favor of #4751