Test PyPI version via CI

[luigibonati]

Description

Improve continuos integration via github actions and test also the PyPI version to identify dependency issues as in #143.
Suggested by @andrrizzi in #144

Todos

Notable points that this PR has either accomplished or will accomplish.

• create new workflow for PyPI version
  • Install mlcolvar from pip
  • checkout to latest tag
• update CI to use latest actions (checkout/v4)

Status

• Ready to go

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 92.35%. Comparing base (8dff46b) to head (c765985).

Additional details and impacted files

[luigibonati]

I set up the tests and, with the latest pypi release, they are working correctly!
I scheduled them to run weekly

if there are no comments I will merge it