FIX: Warn when bridged interpolation uses bad channels

[Deepnar]

Summary

interpolate_bridged_electrodes temporarily clears inst.info["bads"] while building the interpolation. This can allow channels already marked bad to influence the result without notifying the caller.

This patch keeps the existing interpolation behavior and public API unchanged, but emits a warning naming the affected channels and documents the behavior.

Changes

• Warn when inst.info["bads"] is non-empty.
• Document the behavior in the public docstring.
• Extend the existing regression test to check the warning and restoration of the original bad-channel list.
• Add a bugfix changelog fragment.

Testing

• .venv/bin/python -m pytest -p no:pytest-qt mne/preprocessing/tests/test_interpolate.py::test_interpolate_bridged_electrodes --verbose — 1 passed
• .venv/bin/python -m pytest -p no:pytest-qt mne/preprocessing/tests/test_interpolate.py --verbose — 11 passed
• .venv/bin/python -m pytest -p no:pytest-qt mne/tests/test_docstring_parameters.py --verbose — 17 passed, 2 skipped
• Ruff check and format check passed
• Codespell passed
• git diff --check passed

Closes #14263.

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