refactor: avoid stringified type hints

[romanc]

Description

The future is here. We don't have to rely on stringified type hints anymore. Instead, we can use from __future__ import annotations to have python parse the code twice (once to register all types and then another time to actually check).

How Has This Been Tested?

All good as long as CI is still green.

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas: N/A
• I have made corresponding changes to the documentation: N/A
• My changes generate no new warnings
• Any dependent changes have been merged and published in downstream modules: N/A
• New check tests, if applicable, are included: N/A

[FlorianDeconinck]

LGTM

"The future is here". Nice.