Make sure t0 filter is zero-area

[iguinn]

Fixed normalization of triangle and throw error if length of kernel is incorrect

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 3 lines in your changes missing coverage. Please review.

Project coverage is 60.39%. Comparing base (dae9ccb) to head (905e1a8).
Report is 8 commits behind head on main.

Files with missing lines	Patch %	Lines
src/dspeed/processors/kernels.py	0.00%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #103      +/-   ##
==========================================
- Coverage   60.42%   60.39%   -0.04%     
==========================================
  Files          51       51              
  Lines        3467     3469       +2     
==========================================
  Hits         2095     2095              
- Misses       1372     1374       +2     

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