Configure coverage to omit tests

[oesteban]

Summary

• add a [tool.coverage] section in pyproject.toml so that test files are not
  included in coverage reports

Testing

• pip install -e .[tests]
• TEST_DATA_HOME=/tmp/testdata pytest -q (fails: FileNotFoundError for someones_bspline_coefficients.nii.gz)

---

https://chatgpt.com/codex/tasks/task_e_6879d623d50c83308df8c9faaad659fb

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 94.98%. Comparing base (33d4af8) to head (bedabae).
Report is 12 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #244      +/-   ##
==========================================
- Coverage   95.55%   94.98%   -0.58%     
==========================================
  Files          30       16      -14     
  Lines        3063     1833    -1230     
  Branches        0      236     +236     
==========================================
- Hits         2927     1741    -1186     
+ Misses        136       76      -60     
- Partials        0       16      +16     

Flag	Coverage Δ
unittests	94.84% <ø> (-0.50%)	⬇️

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