fix(api): Validate per_page lower bound

[lobsterkatie]

In our base endpoint class, we check the incoming per_page parameter against an upper bound, but we don't currently check it against a lower bound... until we go to actually use it, at which point we error out with a generic 500 response (rather than the more helpful and explanatory 400 generated by per_page values which are too high).

This fixes that by checking the lower bound alongside the upper bound.

Note: The changes in test_base.py look bigger than they are. Really the only new thing is the test_per_page_too_low test. The rest is just a) giving the per_page tests more specific names, and b) moving the invalid cursor test so all of the per_page tests are together.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

✅ All tests successful. No failed tests found.

Additional details and impacted files

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##           master   #83075      +/-   ##
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- Coverage   87.59%   87.58%   -0.01%     
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  Lines      536407   536411       +4     
  Branches    21120    21120              
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- Hits       469839   469822      -17     
- Misses      66209    66230      +21     
  Partials      359      359