Add static typing support

[headtr1ck]

Closes: #1298

Lots of this PR was stolen from #1279

Notice: I intentionally reversed the import behavior of __init__.py and _netCDF4.pyx in the stubs. This should be more in line in how people are using netCDF4. And while doing so I also removed the "._netCDF4" part of the classname in the reprs.

The current typing is working with python 3.11.
TODO:

• Make typing pass with python 3.8 (aka. minimum supported version)

[CLAassistant]

All committers have signed the CLA.

[jswhit]

Thanks! Looks good - but why did you add a new workflow to run stubtest, instead of adding the extra test to the existing workflows?

[headtr1ck]

why did you add a new workflow to run stubtest, instead of adding the extra test to the existing workflows?

Good question. I just took the changes from the previous PR #1279

After the holidays I can continue to work on this and use the existing workflows.

[jswhit]

Looks you like need to add git submodule update --init --recursive after the git clone in stubtest.yml.

[Woefie]

I was the author of #1279 , something went wrong with my pr and when I noticed this one was already made. Which is perfectly fine but now this pr has been dead for 5 months.
The only problem I see now with this pr is that mypy was not installed in the the workflow. Could this just be added and move on?
and merge latest version in this branch

[headtr1ck]

Hey, I was just very busy the last months.
I can try to get it to work the next days.

And thanks for your initial work, it was very helpful to get started.