Add tests for Optuna pow2 search space

[mdekstrand]

This adds tests for the pow2 search space, and tightens up some Optuna typing and error reporting.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.56%. Comparing base (b7c2fc1) to head (276f079).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1144   +/-   ##
=======================================
  Coverage   89.55%   89.56%           
=======================================
  Files         256      256           
  Lines       17231    17234    +3     
=======================================
+ Hits        15432    15435    +3     
  Misses       1799     1799           

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