Catch invalid pixel alignments in split_pixels function to prevent neg vals

[olivialynn]

Change Description

Closes #653

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.75%. Comparing base (47e1956) to head (5bfe632).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #675   +/-   ##
=======================================
  Coverage   93.74%   93.75%           
=======================================
  Files          33       33           
  Lines        2062     2064    +2     
=======================================
+ Hits         1933     1935    +2     
  Misses        129      129           

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