Update to use the `referencing` implementation of ref resolution from `jsonschema`

I haven't looked at this since helping kick the tires on the initial version of the new reference resolution behavior.

`check-jsonschema` needs to catch up (and the warning filter in pytest config in `tox.ini` needs to be removed).

This will also require that the lower bound for supported `jsonschema` versions jumps to 4.18.0 or later.