[CLI] Refactor open into pathlib.Path.open

[elpekenin]

Description

As per title.
While doing a PR i noticed a few open(Path, mode) lines which felt a bit off (non-idiomatic), and after looking for open on lib/python i've noticed that code does indeed use this method on most places, so refactored the ones that don't for consistency.

Notes:

• I haven't tested any of the changes yet, will try and do later today. Thus, draft
• I was unsure whether a value was Path or str looking at the code and added a couple type hints on my way to discovery
• On code looking for comments (license headers), shouldn't strip be used instead on rstrip? ie: remove leading -and not trailing- spaces that would make the str.startswith not detect an existing comment

Types of Changes

• Core
• Bugfix
• New feature
• Enhancement/optimization
• Keyboard (addition or update)
• Keymap/layout/userspace (addition or update)
• Documentation

Issues Fixed or Closed by This PR

Checklist

• My code follows the code style of this project: C, Python
• I have read the PR Checklist document and have made the appropriate changes.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• I have tested the changes and verified that they work and don't break anything (as well as I can manage).