Build maintenance

[jcapriot]

PR to handle some azure testing build updates and maintenance.
I'll amend this list with a description of the changes as they go in.

• Updates mamba install script for linux/osx CI
• Drops testing on python 3.7
• Updates doc build to 3.10
• Updates requirements to be consistent with python 3.8 minimum.
• Reformats with black 23.1a1

[codecov]

Codecov Report

Merging #299 (d9bb458) into main (fe6931e) will decrease coverage by 0.05%.
The diff coverage is 100.00%.

❗ Current head d9bb458 differs from pull request most recent head 77a117a. Consider uploading reports for the commit 77a117a to get more accurate results

@@            Coverage Diff             @@
##             main     #299      +/-   ##
==========================================
- Coverage   85.23%   85.19%   -0.05%     
==========================================
  Files          36       38       +2     
  Lines       11239    11266      +27     
==========================================
+ Hits         9580     9598      +18     
- Misses       1659     1668       +9     

Impacted Files	Coverage Δ
discretize/mixins/mesh_io.py	90.90% <100.00%> (+0.03%)	⬆️
discretize/__init__.py	59.09% <0.00%> (ø)
discretize/base/__init__.py	100.00% <0.00%> (ø)
discretize/mixins/mpl_mod.py	72.52% <0.00%> (+0.02%)	⬆️

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