test: ensure everything works with minimal declared dependencies, test all examples

[tlambert03]

fixes #697

This PR

1. Tests all of the examples in our docs/examples folder to make sure they run without error
2. Adds a test group that uses only the minimal stated dependencies, so that we're not polluted by "optional" dependencies

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 89.28%. Comparing base (6179a0d) to head (fc5069f).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #702      +/-   ##
==========================================
+ Coverage   88.73%   89.28%   +0.54%     
==========================================
  Files          40       40              
  Lines        4812     4816       +4     
==========================================
+ Hits         4270     4300      +30     
+ Misses        542      516      -26     

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