Updates for release 0.8.0

[jcapriot]

Introduces __all__ for public API definition in EM modules to clarify intended usage.

Adds a new kernels module and integrates it into documentation.

Updates release workflow to install the package with extensions and build documentation.

Minor fixes and improvements to the documentation build process.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 83.85%. Comparing base (2319f14) to head (77127a8).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #85      +/-   ##
==========================================
+ Coverage   83.75%   83.85%   +0.10%     
==========================================
  Files          31       31              
  Lines        3146     3166      +20     
  Branches      267      267              
==========================================
+ Hits         2635     2655      +20     
  Misses        443      443              
  Partials       68       68              

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