CI updates, use RTD docs theme etc.

[sk1p]

Contributor Checklist:

• I have added myself to the creators.json file
• I have added a changelog entry for my contribution
• I have added/updated documentation for all user-facing changes
• I have added/updated test cases

[codecov]

Codecov Report

Base: 59.92% // Head: 59.38% // Decreases project coverage by -0.54% ⚠️

Coverage data is based on head (61ca5bb) compared to base (f196683).
Patch has no changes to coverable lines.

❗ Current head 61ca5bb differs from pull request most recent head c8e8f34. Consider uploading reports for the commit c8e8f34 to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #70      +/-   ##
==========================================
- Coverage   59.92%   59.38%   -0.55%     
==========================================
  Files           8        8              
  Lines         549      549              
  Branches       67       66       -1     
==========================================
- Hits          329      326       -3     
- Misses        206      208       +2     
- Partials       14       15       +1     

Impacted Files	Coverage Δ
src/ptychography40/reconstruction/ssb/udf.py	60.80% <0.00%> (-2.41%)	⬇️

Help us with your feedback. Take ten seconds to tell us how you rate us. Have a feature suggestion? Share it here.

☔ View full report at Codecov.
📢 Do you have feedback about the report comment? Let us know in this issue.

[uellue]

LGTM, thx! :-)