feat: make it possible to create v2 fragments using the fragment API

[westonpace]

Previously it was ignoring the use_legacy_format option

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 84.21053% with 9 lines in your changes missing coverage. Please review.

Project coverage is 79.77%. Comparing base (63227f4) to head (9869ffc).

Files	Patch %	Lines
rust/lance/src/dataset/fragment/write.rs	84.21%	0 Missing and 9 partials ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2534   +/-   ##
=======================================
  Coverage   79.76%   79.77%           
=======================================
  Files         207      207           
  Lines       59586    59643   +57     
  Branches    59586    59643   +57     
=======================================
+ Hits        47528    47578   +50     
+ Misses       9264     9257    -7     
- Partials     2794     2808   +14     

Flag	Coverage Δ
unittests	79.77% <84.21%> (+<0.01%)	⬆️

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