Fix lint checks and patch targets that look like ints

[jg-rp]

This PR fixes some lint checks and ensures JSON Patch targets are strings if they are operating on a mapping.

Previously,

assert JSONPatch().add(path="/1", value=99).apply({"foo": 1}) == {"foo": 1, 1: 99}

now, the new 1 is a string:

assert JSONPatch().add(path="/1", value=99).apply({"foo": 1}) == {"foo": 1, "1": 99}