Refactor tests to use fixtures

[fivegrant]

What this PR does

The WET tests are taken and made DRY by using fixtures. This is done by

1. Moving repeated logic into conftest.py
2. Merging all unit tests into a single file
3. Creating resource directories for each test

In the future, the basic tests for each operation can be easily refactored so we can evaluate over input.

What this PR does NOT do

1. Test live
2. Test qualitatively

Additionally, I think the current assertions are not super strong as tests. Better assertions are needed.

[codecov]

Codecov Report

Merging #18 (64c216a) into main (2c32c25) will increase coverage by 1.84%.
Report is 3 commits behind head on main.
The diff coverage is 97.87%.

@@            Coverage Diff             @@
##             main      #18      +/-   ##
==========================================
+ Coverage   81.78%   83.62%   +1.84%     
==========================================
  Files           5        6       +1     
  Lines         505      519      +14     
==========================================
+ Hits          413      434      +21     
+ Misses         92       85       -7     

Files Changed	Coverage Δ
api/utils.py	79.03% <85.71%> (+4.42%)	⬆️
api/server.py	95.45% <100.00%> (+4.68%)	⬆️
lib/settings.py	100.00% <100.00%> (ø)
worker/operations.py	75.21% <100.00%> (ø)
worker/utils.py	91.22% <100.00%> (ø)

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