Add Labels.find and Labels.video

[talmo]

This PR adds Labels.find() and Labels.video following the core SLEAP implementations.

Note: Since we don't have a labels cache, the Labels.find() implementation will be highly inefficient for many query types or datasets.

[codecov]

Codecov Report

Merging #35 (413c3f7) into main (f0adca7) will increase coverage by 0.14%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main      #35      +/-   ##
==========================================
+ Coverage   94.37%   94.52%   +0.14%     
==========================================
  Files          12       12              
  Lines         996     1022      +26     
==========================================
+ Hits          940      966      +26     
  Misses         56       56              

Impacted Files	Coverage Δ
sleap_io/__init__.py	100.00% <100.00%> (ø)
sleap_io/model/labels.py	100.00% <100.00%> (ø)

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