Use nbval to execute notebooks and precommit with nbqa for linting notebooks

[maximlt]

For some reason the CI would not even start running on https://github.com/holoviz/hvplot/pull/705.

[MridulS]

@maximlt the test failures don't seem related to the changes. I have added pre-commit here to do linting and test on github actions. This will also let us move other flake linting tests to pre-commit and sunset using doit test_flakes.

[maximlt]

@MridulS sorry for taking so long to come back to your PR!

Unfortunately it seems that there's a problem. As is the examples tests hang on windows and the workflows fail after they time out. As a test in the previous commit I directly ran nbval in the workflow instead of having it being executed by doit/pyctdev. That attempt succeeded. So there's something happening when doit/pyctdev runs nbval, that causes the examples tests to hang.

I'd be really happy to see nbsmoke replaced by nbval, and this throughout all the HoloViz maintained projects, however this looks like a blocker; pyctdev is as far as I know the interface we would like to use to manage all these projects (cc @jbednar ).

Let me know if you have any idea how to debug this.

[maximlt]

Superseded by yet another PR: https://github.com/holoviz/hvplot/pull/1044

Thanks for your initial push on that @MridulS, it finally worked, the tests are no longer hanging on Windows!