fix: channel splitting for multi-channel model predictions

[alexander-held]

#303 introduced a bug in model_utils.prediction when used with multi-channel models. The split of yields into channels was happening at the wrong depth after this refactor. This update fixes the bug, and changes the corresponding test to catch such an issue.

* fixed channel splitting for multi-channel model predictions
* updated pre-commit

[codecov]

Codecov Report

Merging #312 (03b44cb) into master (9eb92b6) will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##            master      #312   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           23        23           
  Lines         1873      1873           
  Branches       304       304           
=========================================
  Hits          1873      1873           

Impacted Files	Coverage Δ
src/cabinetry/model_utils.py	100.00% <ø> (ø)

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