Add an option to use uv venv and uv pip in the python and poetry plugins

[lengau]

What needs to get done

This old experimental PR is an example: #825

You should be able to make parts like:

parts:
  python:
    source: .
    python-package-manager: uv
  poetry:
    source: .
    poetry-package-manager: uv

and instead of using the system python -m venv and installing pip in that virtual environment, it would use uv for the relevant venv and pip commands.

Why it needs to get done

The old methods are both slow and can be error-prone since the behaviour of venv and pip changes from base to base.