Drop packaging options other than `uv`

[alexdewar]

Following a discussion on Teams, it seems that everyone is on board with us moving to uv for packaging and dropping the poetry and pip-tools options.

This should make the templating simpler and more maintainable.

Things to do:

1. Remove files and parts of files that are only relevant to the pip-tools and poetry packaging options
2. Remove CI workflows for poetry and pip-tools packaging options
3. Update README. We should tell users to install uv. Once they've done that, they can invoke cookiecutter with uvx without installing it directly 😄
4. (Optionally) change the the dev-requirements.txt in the root to a pyproject.toml instead (with uv in non-package mode)
5. (Optionally) add pre-commit hook to ensure uv.lock is up to date

Bear in mind #529 when doing this. I think we should follow @AdrianDAlessandro's suggestion and just install the dependencies with uv add with a hook.