[Parsiffall1]

Fixes #637.

mocker.patch and friends install a side_effect on the mock's __enter__ that warns about using the mock as a context manager. mocker.resetall(side_effect=True) resets the side_effect of child mocks too, so after it the warning was gone:

def test_cm(mocker):
    mocked = mocker.patch("json.loads")
    mocker.resetall(side_effect=True)
    with mocked:  # no PytestMockWarning
        pass

_start_patch now records the original __enter__ child and its warning hook on the cache item, and resetall puts the hook back after resetting, the same way it already restores the side_effect of spies. Because the original child is kept rather than looked up again, a __enter__ the user deleted or replaced is left alone. patch.context_manager never had the hook, so nothing changes there.

Tests added to TestContextManagerWarnings:

• the warning survives resetall(return_value=True, side_effect=True) for mocker.patch;
• the same for a spy backed by a MagicMock, which still calls through;
• patch.context_manager still does not warn after resetall;
• resetall(side_effect=True) does not fail after del mocked.__enter__.

The first two fail on main; the last one covers the deleted __enter__ case of the fix itself. tox -e py313,py314,norewrite passes (172 passed; norewrite 155 passed, 17 expected skips), and pre-commit passes on the changed files. A changelog entry is included.