STY: Add type hints to PET-related classes and functions

[jhlegarreta]

Add type hints to PET-related classes and functions.

[jhlegarreta]

I left data.PET.to_nifti out as when adding type hinting for the existing parameters mypy complained in important ways about it deviating from the base class signature. So, it needs refactoring. Outside the scope of this PR.

[jhlegarreta]

Failures:

src/nifreeze/model/pet.py:163: error: Argument 1 to "design_matrix" of "BSpline" has incompatible type "float"; expected "_CanArrayND[floating[Any] | integer[Any] | bool_] | Sequence[float | floating[Any] | integer[Any] | bool_]"  [arg-type]

and

src/nifreeze/estimator.py:269: error: Argument 1 to "fit_predict" of "PETModel" has incompatible type "ndarray[Any, Any] | None"; expected "int | None"  [arg-type]

So, the second one is related to the fact that fit_predict expects an int for the index but lofo_split returns an array for test_time.

[codecov]

Codecov Report

❌ Patch coverage is 94.44444% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 75.71%. Comparing base (4cfaadb) to head (ff4a9fa).

Files with missing lines	Patch %	Lines
src/nifreeze/data/pet.py	90.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #189      +/-   ##
==========================================
+ Coverage   75.64%   75.71%   +0.06%     
==========================================
  Files          24       24              
  Lines        1433     1437       +4     
  Branches      166      166              
==========================================
+ Hits         1084     1088       +4     
  Misses        276      276              
  Partials       73       73              

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[jhlegarreta]

I am leaving out lofo_split and other problematic ones for the sake of moving forward. lofo_split is anyways likely to be removed by PR #203. So adding type hints to those/issues will be addressed in future PRs.

[jhlegarreta]

Merging. Checked that the output of the notebook is the same that we get prior to the change (modulo slight differences at the beginning/end of the sequence: x-ref #204 (comment)):

Wanted to make sure due to these changes:
https://github.com/nipreps/nifreeze/pull/189/files#diff-cf38fd0d1c160d335eaf2315eb3076ecbb8e99d387b5f642571190c033a0e5beR122
https://github.com/nipreps/nifreeze/pull/189/files#diff-cf38fd0d1c160d335eaf2315eb3076ecbb8e99d387b5f642571190c033a0e5beR164