Clean up handling of tests

[blink1073]

PyTest recommends putting your tests at the top level, and in fact we are having trouble in running our tests from the installed package in CI.

• Move the tests folder to the top level
• Include the tests folder in the sdist but not the wheel
• In CI, unpack the sdist and run pytest from the sdist

Left to do:

• Get all tests passing
• Update the conda recipe to actually run the tests in the tests directory (needs a new release)
• Update docs

[codecov-commenter]

Codecov Report

Merging #700 (cd8656f) into main (745f5ba) will decrease coverage by 7.01%.
The diff coverage is n/a.

❗ Current head cd8656f differs from pull request most recent head b989c28. Consider uploading reports for the commit b989c28 to get more accurate results

@@            Coverage Diff             @@
##             main     #700      +/-   ##
==========================================
- Coverage   77.97%   70.95%   -7.02%     
==========================================
  Files         115       62      -53     
  Lines       10817     7486    -3331     
  Branches     1465     1185     -280     
==========================================
- Hits         8435     5312    -3123     
+ Misses       1981     1817     -164     
+ Partials      401      357      -44     

Impacted Files	Coverage Δ
tests/auth/test_authorizer.py
tests/auth/test_login.py
tests/auth/test_security.py
tests/auth/test_utils.py
tests/conftest.py
tests/extension/mockextensions/__init__.py
tests/extension/mockextensions/app.py
tests/extension/mockextensions/mock1.py
tests/extension/mockextensions/mock2.py
tests/extension/mockextensions/mock3.py
... and 43 more

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