draft: ignore sign bit when all value are negative

[thinh2]

Implementation for #2714 .

[github-actions]

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[codecov-commenter]

Codecov Report

Attention: Patch coverage is 65.51724% with 10 lines in your changes missing coverage. Please review.

Project coverage is 77.83%. Comparing base (3f935d5) to head (214a8b7).

Files with missing lines	Patch %	Lines
...t/lance-encoding/src/encodings/physical/bitpack.rs	65.38%	9 Missing ⚠️
rust/lance-encoding/src/encodings/physical.rs	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2912      +/-   ##
==========================================
- Coverage   77.83%   77.83%   -0.01%     
==========================================
  Files         231      231              
  Lines       70199    70219      +20     
  Branches    70199    70219      +20     
==========================================
+ Hits        54641    54656      +15     
+ Misses      12691    12679      -12     
- Partials     2867     2884      +17     

Flag	Coverage Δ
unittests	77.83% <65.51%> (-0.01%)	⬇️

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[westonpace]

Looks straightforward to me. @albertlockett any thoughts?