Improve sparse and logarithmic testing

[gdalle]

No description provided.

[codecov]

Codecov Report

Patch coverage: 58.33% and project coverage change: +15.02% 🎉

Comparison is base (dd148cc) 78.27% compared to head (d7d6796) 93.29%.

Additional details and impacted files

@@             Coverage Diff             @@
##             main      #42       +/-   ##
===========================================
+ Coverage   78.27%   93.29%   +15.02%     
===========================================
  Files          18       18               
  Lines         474      537       +63     
===========================================
+ Hits          371      501      +130     
+ Misses        103       36       -67     

Files Changed	Coverage Δ
src/inference/forward_backward.jl	96.90% <ø> (+9.55%)	⬆️
src/utils/lightdiagnormal.jl	100.00% <ø> (+100.00%)	⬆️
src/utils/probvec.jl	100.00% <ø> (+10.00%)	⬆️
src/utils/transmat.jl	93.33% <ø> (+19.64%)	⬆️
src/utils/check.jl	78.04% <54.54%> (+1.12%)	⬆️
src/inference/baum_welch.jl	90.69% <100.00%> (+8.19%)	⬆️

... and 10 files with indirect coverage changes

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