MNT: switch to mamba-org/setup-micromamba, split CI tests

[kmuehlbauer]

• [x] Closes #115
• [x] Changes are documented in history.md

[codecov[bot]]

Codecov Report

Merging #116 (976ef25) into main (6fe2ea0) will decrease coverage by 0.03%. The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #116      +/-   ##
==========================================
- Coverage   88.08%   88.05%   -0.03%     
==========================================
  Files          19       19              
  Lines        3297     3299       +2     
==========================================
+ Hits         2904     2905       +1     
- Misses        393      394       +1     

Flag	Coverage Δ
unittests	88.05% <100.00%> (-0.03%)	:arrow_down:

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
xradar/io/backends/rainbow.py	92.10% <100.00%> (-0.21%)	:arrow_down:

[kmuehlbauer]

@mgrover1 When you get to it, could you have a look at this and merge, if you are fine with it?

• provision-with-micromamba is deprecated in favor of the new setup-micromamba
• unittests and notebooktests are split for better maintainability

[mgrover1]

Great! Thanks @kmuehlbauer