[OTHER] Update `os.path` to `pathlib.Path`

[teald]

os.path (and related utilities from the os module) should be replaced by pathlib.Path and its higher-level API where performance is not a concern.

Notes

• As far as I know there are not issue with performance related to this. In other words, there is no place where os.path is used that using Path/its API instead would incur noticeable performance costs.
• In cases where that may be the case, it's almost always the case the os.path is being called on a path string that is usually using os.path.join anyways.
  • In some cases, this can be extracted from loops (examples?).
• I'm unsure if performance is still a concern here; the bottom line is that Path is easier to support than str + os.path.
• This can be enabled as a ruff linter ruleset (PTH), which is currently disabled.