Refactors DirectEnums to uppercase

[georgeyiasemis]

Refactors attributes of DirectEnum-derived classes to uppercase.

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 89.87342% with 8 lines in your changes are missing coverage. Please review.

Project coverage is 84.08%. Comparing base (b56a724) to head (97d8909).

Files	Patch %	Lines
direct/data/mri_transforms.py	84.44%	7 Missing :warning:
direct/nn/get_nn_model_config.py	85.71%	1 Missing :warning:

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #266      +/-   ##
==========================================
+ Coverage   84.05%   84.08%   +0.02%     
==========================================
  Files          93       93              
  Lines        6486     6504      +18     
==========================================
+ Hits         5452     5469      +17     
- Misses       1034     1035       +1     

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