Download data simultaneously and cache files

[yndevops2]

This update speeds up downloading ERA5 data by letting you download multiple files at once. It also adds caching for downloaded data and a progress bar to track the download status.

[lkstrp]

Hey @yndevops2,
all merging issues should be resolved now. Sorry for the late response, this will be better from now on. You don't need to create an extra issue for those things, just ping me here.

Please give me a bit more time to review your PR. I will test it soon. Thank you !

[yndevops2]

Still issue with codecov.
Could you please help me?

[lkstrp]

There have been some changes to the tests which might messed up your report. But that should be fine now.
To resolve the failing Code Cov you need to provide tests for your newly created functions. Check the full Codecov Report which points you to which lines need additional tests. You can implement them in /test (we use pytest).

[yndevops2]

This is first time for the CodeCov.
So if you can help me for that, that would be great help for me!!!!