Refactor JSON Patch OpRemove and OpMove

[jg-rp]

This PR refactors OpRemove and OpMove to use a common _remove() function for consistency and better code reuse, just like we did with _add() in #136.

OpReplace does not use _remove() due to its distinct behavior when replacing a JSON root value.

[carlitogwapito]

A small optional test-only commit, based directly on this branch.

The shared helper now rejects a move from a MappingProxyType or tuple. The old implementation writes the destination without removing anything from those read-only sources, so it behaves like a copy.

Two small guards worth keeping: reject the read-only source, and leave the destination unchanged on that rejection. This doesn't assume apply() is atomic for other failures.

Checked on Python 3.14.4: both new cases pass your head and catch the old copy-like behavior; the existing move-to-root and array-append tests pass on both. Focused Ruff lint/format passes. I haven't run the full Hatch/compliance suites, typing, build or optional-regex/version/OS matrix.

To run the added file in your tree: python -m pytest tests/test_move_readonly_source.py -q.