fix(image): validate slice count before subtraction

[lguerard]

• Added a check to ensure both images have the same number of slices.
• Exits with an error message if the slice counts differ.
• Adjusted the subtraction operation to handle stack images appropriately.

[codecov]

Codecov Report

❌ Patch coverage is 0% with 5 lines in your changes missing coverage. Please review.
✅ Project coverage is 25%. Comparing base (420eb59) to head (0a46264).
⚠️ Report is 3 commits behind head on devel.

Files with missing lines	Patch %	Lines
src/imcflibs/imagej/misc.py	0%	5 Missing ⚠️

Additional details and impacted files

@@         Coverage Diff          @@
##           devel   #117   +/-   ##
====================================
- Coverage     25%    25%   -0%     
====================================
  Files         25     25           
  Lines       1690   1694    +4     
====================================
  Hits         421    421           
- Misses      1269   1273    +4     

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