chore: pin pytest and dedupe dependency groups

[d-v-b]

pins pytest to an exact version (which resolves recent test failures) and deduplicates our dependency group specification.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (2a0b67f) to head (070de02).

Additional details and impacted files

@@             Coverage Diff              @@
##             main      #844       +/-   ##
============================================
+ Coverage   40.28%   100.00%   +59.71%     
============================================
  Files          27        27               
  Lines         901       901               
============================================
+ Hits          363       901      +538     
+ Misses        538         0      -538     

see 26 files with indirect coverage changes

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[d-v-b]

i'm leaving the pytest pin, but this PR also requires changes to our test fixtures to avoid deprecation warnings in pytest 9.x. those changes do not reduce test efficacy.

[d-v-b]

the i386 test will be failing, but that's resolved by #845, which I will merge next. So I'm going to merge this despite checks failing.