TYP: enable mypy check_untyped_defs for shap/maskers/_image - #4761

Summary

• Adds type annotations to all functions and classes in shap/maskers/_image.py
• Removes shap.maskers._image from the check_untyped_defs = false override in pyproject.toml
• mypy shap/maskers/_image.py passes with zero new errors (only the pre-existing numba.njit attr-defined error shared with _clustering.py and _masked_model.py, which disappears in CI where numba is not installed)

Changes

shap/maskers/_image.py

• from __future__ import annotations + numpy.typing as npt added
• Class-level variable declarations added so _blur_value_cache is typed as npt.NDArray[Any] | None rather than inferred as None
• __init__ annotated; int(np.prod(...)) wrap added (returns np.intp, base class expects int); targeted # type: ignore for issubclass-based guard (mypy cannot narrow on issubclass, changing to isinstance would be a behavior change) and for tuple(map(int, ...)) returning variable-length tuple
• assert self._blur_value_cache is not None added before index access — logically safe (the if self.last_xid != id(x) block above always assigns it), narrows the type for mypy
• __call__ annotated with x: Any (accepts torch.Tensor + ndarray), mask: npt.NDArray[Any] | bool | None, # type: ignore[override] since base class does not allow None mask
• inpaint, build_partition_tree, save, load annotated
• _jit_build_partition_tree annotated with # type: ignore[misc] on @njit (project convention, same as _clustering.py)

pyproject.toml

• "shap.maskers._image" commented out following the existing # NOW TYPE CHECKED convention

Test

.venv/bin/mypy shap/maskers/_image.py --no-error-summary 2>&1 | grep "_image.py"
# shap/maskers/_image.py:10: error: Module "numba" has no attribute "njit"  [attr-defined]
# (pre-existing, shared with _clustering.py and _masked_model.py, gone in CI)

AI Disclosure

Type annotations were drafted with AI assistance (Claude) and verified manually against the source code and mypy output.

Part of #3730.