feat: monorepo

[nstarman]

Ok. This is a big change.
Now optional dependencies are split into separate packages so that the heaps of interoperability code do not have to live inside galax main.
We can release the companion packages onto PyPI and keep them in lock-step with galax since they share the same VCS.
The packages now are:

`galax` <- `galax-interop-astropy`  <- `galax-suite`
        <-  `galax-interop-gala`    <—|

It's equivalent to galax[interop-all], but galax-suite suite exists to 1) collect all packages into one obvious suite 2) Easy testing.

Also this monorepo will eventually enable us to have separate testing badges for each library!

See https://github.com/manuel-koch/hatch-monorepo-sandbox for the layout.

[nstarman]

Diagnosing test failures:

• CD is failing because galax-suite is building into src, which is triggering "W005: Wheel contains common toplevel name in library: src/". We kind of want it to build to src, but have it packaged into a different name. galax-suite then ends up being an implicit namespace package, which is very convenient.
• tests are failing because they can't find a version of galax-interop-astropy. This is more pernicious. There's a released version of galax, but not of galax-interop-astropy. Since versioning depends on the git tag, I'm not sure how we get these tests passing in a branch!