Use MifImage class instead of mrconvert

[tsalo]

Keeping as a draft for now.

I've opened nipy/nibabel#1489 to add the MifImage class to nibabel. Depending on how quickly that PR progresses, we might want to keep copies of the class in ModelArrayIO for a release or two.

NOTE: Since HBCD does not include fixel data, this is a low priority item.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 77.05382% with 81 lines in your changes missing coverage. Please review.
✅ Project coverage is 75.76%. Comparing base (dd8cd8a) to head (a2cc521).

Files with missing lines	Patch %	Lines
src/modelarrayio/utils/mif.py	77.74%	40 Missing and 35 partials ⚠️
src/modelarrayio/cli/h5_to_mif.py	62.50%	6 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #43      +/-   ##
==========================================
+ Coverage   69.10%   75.76%   +6.66%     
==========================================
  Files          17       17              
  Lines        1162     1465     +303     
  Branches      211      288      +77     
==========================================
+ Hits          803     1110     +307     
+ Misses        295      256      -39     
- Partials       64       99      +35     

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