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

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

Start at the boundary where tasks and their paths are pickled before being sent to the remote worker, then trace how dependencies and products are included. The work is done when all paths crossing that boundary are converted to PurePaths and cross-platform remote execution no longer depends on the originating platform; review the referenced CPython pull request for relevant behavior.