CR #6

[ryan-williams]

A few changes I accumulated while reading #6 (merging this PR will update #6):

• I don't think we need the dependency on attrs; dataclasses does what we need, in the stdlib
• Specify 3.11 for pre-commit tools in pyproject.toml (to match GHA)
• Use SOMA_JOINID instead of "soma_joinid"
• Some suggested type-alias/comment/docstring tweaks

The commits should be relatively self-contained, in case that's an easier way to browse the changes in isolation.

I don't feel strongly about these, happy to discuss!

[bkmartinjr]

Two questions (attrs and SOMA_JOINID), but otherwise these are all great changes. Lets sort out the aforementioned two offline.