Support pathlib.Path objects for GISDocument and other interfaces

[mfisher87]

Thanks @matthewfeickert for calling attention to this!

This should function the same as if we passed str(path) to GISDocument, but we get an error

from jupytergis_lab import GISDocument
from pathlib import Path

path = Path.cwd() / "france_hiking.jGIS"
path.is_file()

doc = GISDocument(path)
doc

File /home/shared/jupytergis/.venv/lib/python3.10/site-packages/jupyter_client/jsonutil.py:192, in json_clean(obj)
    189     return obj.strftime(ISO8601)
    191 # we don't understand it, it's probably an unserializable object
--> 192 raise ValueError("Can't clean for JSON: %r" % obj)

ValueError: Can't clean for JSON: PosixPath('[/home/shared/jupytergis/examples/france_hiking.jGIS](http://localhost:8888/lab/tree/RTC%3Aexamples/examples/france_hiking.jGIS)')

[matthewfeickert]

Thanks for opening up an Issue on this! It would be a small, but nice, quality of life use improvement. :)