Fix bgr-rgb conversion with sleap-render

[gitttt-1234]

This PR fixes the colors in rendered videos by converting annotated frames from BGR to RGB before saving with imageio (default in sleap-io).

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 59.46%. Comparing base (1454e2e) to head (b16bcd4).
⚠️ Report is 1 commits behind head on develop.

Additional details and impacted files

@@           Coverage Diff            @@
##           develop    #2444   +/-   ##
========================================
  Coverage    59.45%   59.46%           
========================================
  Files           68       68           
  Lines        13219    13222    +3     
========================================
+ Hits          7859     7862    +3     
  Misses        5360     5360           

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