raise error if decoding hash fails during inclusion proof

[bobcallaway]

if the decoding of a hexadecimal string were to fail, we should raise the error instead of squelching it and returning a proof failure (since the underlying value would be nil).

[codecov]

Codecov Report

❌ Patch coverage is 33.33333% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 26.17%. Comparing base (488eb97) to head (ca324da).
⚠️ Report is 636 commits behind head on main.

Files with missing lines	Patch %	Lines
pkg/verify/verify.go	33.33%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #2754       +/-   ##
===========================================
- Coverage   66.46%   26.17%   -40.29%     
===========================================
  Files          92      191       +99     
  Lines        9258    20129    +10871     
===========================================
- Hits         6153     5269      -884     
- Misses       2359    14031    +11672     
- Partials      746      829       +83     

Flag	Coverage Δ
e2etests	49.49% <33.33%> (+1.93%)	⬆️
unittests	16.72% <33.33%> (-30.97%)	⬇️

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