Hi, this PR is quite all encompassing but each commit should be roughly standalone.
Please feel free to remove or change anything here or split it into multiple PRs. I'm also happy to do that.

My aim was to make numba-scipy easier to update and work for my purposes (py3.12 #101 , newer scipy etc). The PR itself does a few things

1. Move the project to using pyproject.toml as this seems to be the standard the python ecosystem is moving towards. This allows for the removal of the requirements file as its covered in the pyproject.toml.
2. Move the project to using hatch. This is mainly for versioning reasons, it allows the removal of versioneer and _version.py and both the setup.{py,cfg} . There is a _version.py file is automatically created on install that shouldnt be tracked.
3. To consolidate as much as possible into the pyproject.toml use ruff for linting (and formatting as its there). This moves the contents of .flake8 into the pyproject.toml. 1 less file == better IMO.
4. Fix sphinx build, part of fix readthedocs config and add to CI matrix #104, I havent added it to the CI but that shouldn't be too difficult
5. Upgrade scipy enable dependabot and add a helper action for dependabot to change all scipy version strings in the repo. Aims to close Automatically create PRs that bump the SciPy version. #94

There also seemed to be an unused 'deploy_release.yml'. I've updated this so I think it will now work for uploading to pypi.

Thanks!