Update docs

[joschkabirk]

Summary

This pull request introduces the following changes

• Adds a copy-button to all code cells in the documentation. Example:

• Updates to the lates version of the sphinx theme we are using
• Remove unused sphinx extensions
• Fix some copy-paste errors

Conformity

• Changelog entry
• Documentation

[codecov-commenter]

Codecov Report

Merging #131 (84116bb) into main (bf74557) will not change coverage.
The diff coverage is 100.00%.

❗ Current head 84116bb differs from pull request most recent head 5ec22c8. Consider uploading reports for the commit 5ec22c8 to get more accurate results

@@           Coverage Diff           @@
##             main     #131   +/-   ##
=======================================
  Coverage   95.78%   95.78%           
=======================================
  Files          23       23           
  Lines        2206     2206           
=======================================
  Hits         2113     2113           
  Misses         93       93           

Impacted Files	Coverage Δ
puma/tests/test_line_2D.py	100.00% <100.00%> (ø)

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