feat: add an all null column as a metadata-only operation

[albertlockett]

fixes: #3044

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 94.27313% with 13 lines in your changes missing coverage. Please review.

Project coverage is 78.69%. Comparing base (62a2256) to head (4771984).

Files with missing lines	Patch %	Lines
rust/lance/src/dataset/schema_evolution.rs	91.55%	0 Missing and 13 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3391      +/-   ##
==========================================
+ Coverage   78.65%   78.69%   +0.03%     
==========================================
  Files         250      250              
  Lines       90507    90734     +227     
  Branches    90507    90734     +227     
==========================================
+ Hits        71187    71401     +214     
+ Misses      16396    16393       -3     
- Partials     2924     2940      +16     

Flag	Coverage Δ
unittests	78.69% <94.27%> (+0.03%)	⬆️

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[wjones127]

Nice work!