core: stdcm: add error when input timings aren't possible

[eckter]

May help with debugging "no solution found" issues

[codecov-commenter]

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Codecov Report

Attention: Patch coverage is 66.66667% with 6 lines in your changes missing coverage. Please review.

Project coverage is 39.07%. Comparing base (02ea460) to head (ea7231d).
Report is 1 commits behind head on dev.

Files with missing lines	Patch %	Lines
...otlin/fr/sncf/osrd/stdcm/graph/STDCMPathfinding.kt	64.70%	4 Missing and 2 partials ⚠️

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Additional details and impacted files

@@             Coverage Diff              @@
##                dev    #9437      +/-   ##
============================================
- Coverage     39.08%   39.07%   -0.01%     
- Complexity     2267     2270       +3     
============================================
  Files          1308     1308              
  Lines         99203    99220      +17     
  Branches       3312     3315       +3     
============================================
- Hits          38774    38772       -2     
- Misses        58466    58484      +18     
- Partials       1963     1964       +1     

Flag	Coverage Δ
core	74.99% <66.66%> (-0.01%)	⬇️
editoast	71.97% <ø> (-0.05%)	⬇️
front	10.32% <ø> (ø)
gateway	2.50% <ø> (ø)
osrdyne	3.29% <ø> (ø)
railjson_generator	87.49% <ø> (ø)
tests	86.71% <ø> (ø)

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