Cleanup notebook deps

[disberd]

this just does some cleanup of the codebase, removes all remaining included notebooks, allowing to remove Markdown, InteractiveUtils and Random as dependencies.

MacroTools is still a dependency because we rely on shortdef for the @addmethod macro.

Some tests were also added to reach 100% coverage (though the last added tests for getting to the paths of @macroexpand and multiple call error from different cells was quite weird, might consider revisiting the underlying functionality)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 100.00%. Comparing base (8b6a000) to head (fe5ec45).

Additional details and impacted files

@@             Coverage Diff             @@
##           master       #53      +/-   ##
===========================================
+ Coverage   99.50%   100.00%   +0.49%     
===========================================
  Files          11        11              
  Lines         813       813              
===========================================
+ Hits          809       813       +4     
+ Misses          4         0       -4     

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