restore opencv-python to a hard dependency

[zacharyburnett]

This PR reverts #126 and #136 and restores opencv-python to a hard dependency in the requirements; this will break certain external user workflows on platforms without a precompiled opencv available.

Checklist

• added entry in CHANGES.rst (either in Bug Fixes or Changes to API)
• updated relevant tests
• updated relevant documentation
• updated relevant milestone(s)
• added relevant label(s)

[codecov]

Codecov Report

Patch coverage: 77.77% and project coverage change: +0.21 🎉

Comparison is base (52beb28) 72.57% compared to head (8625279) 72.79%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #155      +/-   ##
==========================================
+ Coverage   72.57%   72.79%   +0.21%     
==========================================
  Files          29       29              
  Lines        5485     5465      -20     
==========================================
- Hits         3981     3978       -3     
+ Misses       1504     1487      -17     

Impacted Files	Coverage Δ
tests/test_jump.py	65.95% <ø> (+2.99%)	⬆️
src/stcal/jump/jump.py	15.11% <77.77%> (+1.06%)	⬆️

Help us with your feedback. Take ten seconds to tell us how you rate us. Have a feature suggestion? Share it here.

☔ View full report in Codecov by Sentry.
📢 Do you have feedback about the report comment? Let us know in this issue.