Remove --relative-root parameter

[tsalo]

Closes #22.

Changes proposed:

• Remove the --relative-root parameter.
• Add more type limitations to the parsers.
• Make some arguments mutually exclusive.
• Rename conversion CLI files and main functions. This does not impact the actual CLIs.
• Move walkthroughs into the documentation. They will be executable at some point.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 33.92857% with 74 lines in your changes missing coverage. Please review.
✅ Project coverage is 37.90%. Comparing base (85d13b4) to head (5aa030c).

Files with missing lines	Patch %	Lines
src/modelarrayio/cli/h5_to_cifti.py	0.00%	17 Missing ⚠️
src/modelarrayio/cli/h5_to_mif.py	0.00%	17 Missing ⚠️
src/modelarrayio/cli/mif_to_h5.py	0.00%	15 Missing ⚠️
src/modelarrayio/cli/h5_to_nifti.py	0.00%	8 Missing ⚠️
src/modelarrayio/utils/fixels.py	0.00%	6 Missing ⚠️
src/modelarrayio/cli/cifti_to_h5.py	63.63%	4 Missing ⚠️
src/modelarrayio/cli/parser_utils.py	76.47%	2 Missing and 2 partials ⚠️
src/modelarrayio/cli/nifti_to_h5.py	84.61%	2 Missing ⚠️
src/modelarrayio/utils/cifti.py	75.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #26      +/-   ##
==========================================
- Coverage   37.98%   37.90%   -0.08%     
==========================================
  Files          13       13              
  Lines         953      947       -6     
  Branches      134      135       +1     
==========================================
- Hits          362      359       -3     
+ Misses        566      561       -5     
- Partials       25       27       +2     

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