Ensure that local paths are working cross-platform with remote backends.

[tobiasraabe]

Currently, we pickle tasks that contain many paths, including for themselves, dependencies, and products, and send them to a remote machine.

This is not possible across different platforms, which is why Windows users probably need to use WLS.

Plan to fix it:

• Before sending data to the remote worker, convert all paths to PurePaths.

Resources

• There is work in CPython to pickle paths across platforms: https://github.com/python/cpython/pull/116523