Switch from dynamic to static requirements

We could upgrade all the libraries to switch from `requirements.txt` and `optional-requirements.txt` to defining them full inside `pyproject.toml`. I think the actual change implementation isn't too bad through Adabot's extended tooling.

Main concerns are that:
- The current way dependencies are defined is incredibly readable right now
- Existing documentation or guides may explicitly say to download requirements using the file (i.e. `pip install -r requirements.txt`)
- Existing projects such as the screenshot tool or `circup` may explicitly look at `requirements.txt` for requirements.

Happy to do this myself and look into the above before making a final suggestion or recommendation about how viable this is.