Fix cnn training notebook

[jennan]

This PR replace the data accessor of the CNN model training notebook with a WeatherBench2 ERA5 data accessor, and fixes related issues.

[coveralls]

Pull Request Test Coverage Report for Build 17197699384

Details

• 3 of 17 (17.65%) changed or added relevant lines in 1 file are covered.
• 1 unchanged line in 1 file lost coverage.
• Overall coverage increased (+0.005%) to 61.141%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
packages/data/src/pyearthtools/data/download/weatherbench.py	3	17	17.65%

Files with Coverage Reduction	New Missed Lines	%
packages/data/src/pyearthtools/data/download/weatherbench.py	1	23.2%

Totals
Change from base Build 17194498940:	0.005%
Covered Lines:	9454
Relevant Lines:	15037

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💛 - Coveralls

[tennlee]

I'm getting an exception running the notebook, let's discuss tomorrow or early next week?

[jennan]

@tennlee I think the PR is ready. The last changes are:

• Finished rewrite the text to remove outdated comments and some duplicated explanations,
• refreshrate of the Rich progress bar changed to avoid the notebook issues (I was able to reproduce the error),
• I have rerun it completely with a machine with a (laptop gamer) GPU.

I have not fixed the partial download issue but made an issue for this one (#165) that I will address shortly (this week). I don't think that would block this PR.

Given that it is more convenient with a GPU, but runnable without do you still want it moved to the low-hardware requirements section?

[tennlee]

This has a conflict with develop/Gallery, can you please rebase and update?

[jennan]

@tennlee sorry I am not too comfortable rebasing branches once they have been pushed to publicly accessible places, I hope you don't mind the merge instead.