Bump minimum Python to 3.11 and av to 14.0.1

[behackl]

In accordance with https://scientific-python.org/specs/spec-0000/ (which we have at some point loosely discussed to follow), our minimum supported Python version could be bumped to 3.11.

This also bumps the minimum required version of av to at least 14.0.1, while our metadata tests only appear to be fixed and working with 15.0.0, their latest release as of right now.

The PR is a draft for now as some additional cleanup is required; e.g., importlib-metadata can be removed, the dependecies can remove the distinctions for Python 3.10.

TODOs

• [ ] remove importlib-metadata
• [ ] handle typing_extensions?
• [ ] remove CI pipeline for 3.9, 3.10

[chopan050]

Regarding the TODOs:

• [ ] remove importlib-metadata - this one was removed in PR #4490 👍🏼
• [ ] handle typing_extensions? - I believe that this one should be done in a separate PR - I can take care of that later
• [ ] remove CI pipeline for 3.9, 3.10 - aren't those automatically removed after the ci.yml edit?

As Python 3.14 was just released and Python 3.11 is now 3+ years old, if we want to be in accordance with SPEC 0, we'll also have to remove support for 3.11 and bump the minimum version to 3.12...