Merge `setup.cfg` into `pyproject.toml` and use dependency groups

[samcunliffe]

The napari plugin template has got rid of setup.cfg and only has pyproject.toml, so it seems that there's no reason to keep both.

Definition of done

• setup.cfg file's contents are moved into pyproject.toml.
• No change to project metadata.
• Developer (testing, doc,...) dependencies are handled in dependency groups (PEP735)

[jaideepkathiresan]

Hi @samcunliffe, I think i can fix this. Could you assign me with this issue?

[jaideepkathiresan]

Hi @samcunliffe, I believe to have addressed the issue. Could you review my pull request? Thank-you.

[jaideepkathiresan]

Hi @samcunliffe, Thanks for reacting! Just wanted to check in, if you've had a chance to review it and everything looks good, would you mind merging it when convenient? Let me know if there's anything else you'd like me to tweak.
Thank-you.

[samcunliffe]

via #322