Implement dependency groups

[cthoyt]

This PR switches from using optional-dependencies to dependency-groups for several development dependencies

This depends on:

• Add dependency-groups support (PEP-735) tox-dev/tox#3409
• Support for PEP 735 astral-sh/uv#8272
• Install dependency groups in the uv pip interface, i.e., uv pip install --group astral-sh/uv#8590
• Lock dependency groups in the uv pip interface, i.e., uv pip compile --group astral-sh/uv#8969
• Add dependency-group cli flags to uv pip install and uv pip compile (--group, --no-group, --only-group, --all-groups) astral-sh/uv#10861
• add pip-compatible --group flag to uv pip install and uv pip compile astral-sh/uv#11686 (actually incorporated in uv 0.6.8)
• Support for PEP 735 dependency groups readthedocs/readthedocs.org#11766, will be solved by Build: allow partial override of build steps readthedocs/readthedocs.org#11710

[cthoyt]

uv will now support dependency groups via its pip interface as of astral-sh/uv#10861

[cthoyt]

I think we're ready for this with astral-sh/uv#11686