Now in python 3.11 there is a built-in library to interact with toml, it could be applied to avoid installing this dependency.

I haven't been making enough time for nose2 lately, but this PR currently isn't quite in a state that I feel I can merge.
I've needed to take time to offer feedback, since it's close, as far as I'm concerned.

• it needs to be restricted to pyproject.toml, not any toml file
• I think we should be using tomli on py<3.11 and stdlib tomllib on 3.11+ -- partly because tomli is what was ported into tomllib
• ☝️ the dependency on tomli should be conditional on a python_version marker

Those are the main things.

I'm also a little bit concerned in theory that nose2 could be confused and made to crash with certain inputs (namely, TOML-native datetime data, which would manifest as unexpected datetime.datetime objects in the config), but I don't know that the config loading which exists today is sufficiently hardened against these sorts of usages. So I wouldn't worry much about it but it would be nice to check on that, maybe after this or a similar changeset merges.