`.MNSession` filepath error across platforms

[BradyAJohnston]

If a blend file has a related .MNSession from a Windows machine, it can't be rendered from the command line on a non-windows machine.

blender -b ~/Dropbox/blender/tinkering/6een/6EEN_flat.blend -o ~/Desktop/
Blender 4.4.3 (hash 802179c51ccc built 2025-04-29 14:25:11)
Read blend: "/Users/brady/Dropbox/blender/tinkering/6een/6EEN_flat.blend"
Error in bpy.app.handlers.load_post[1]:
Traceback (most recent call last):
  File "/Users/brady/Library/Application Support/Blender/4.4/extensions/vscode_development/molecularnodes/session.py", line 199, in _load
    get_session().load(filepath)
  File "/Users/brady/Library/Application Support/Blender/4.4/extensions/vscode_development/molecularnodes/session.py", line 131, in load
    session = pk.load(f)
              ^^^^^^^^^^
  File "/Applications/Blender.app/Contents/Resources/4.4/python/lib/python3.11/pathlib.py", line 873, in __new__
    raise NotImplementedError("cannot instantiate %r on your system"
NotImplementedError: cannot instantiate 'WindowsPath' on your system

Blender quit

Session should be stored and loaded as relative filepath.