core: stdcm: refactor time data into a new data class

[eckter]

Fix #8587

Now is the time for reviews about these time fields, their name, their structure, their docstrings, and so on

Change summary:

1. Move time-related data from edges and nodes into a new struct
2. Improve how these values are forwarded between nodes and edges
3. Add comments for what still needs to be changed for variable stop times

[codecov-commenter]

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Codecov Report

Attention: Patch coverage is 93.06931% with 7 lines in your changes missing coverage. Please review.

Project coverage is 37.02%. Comparing base (91e7663) to head (6f283c9).
Report is 9 commits behind head on dev.

Files with missing lines	Patch %	Lines
.../main/kotlin/fr/sncf/osrd/stdcm/graph/STDCMEdge.kt	80.00%	1 Missing and 1 partial ⚠️
.../main/kotlin/fr/sncf/osrd/stdcm/graph/STDCMNode.kt	88.23%	1 Missing and 1 partial ⚠️
.../sncf/osrd/stdcm/graph/PostProcessingSimulation.kt	50.00%	1 Missing ⚠️
...in/fr/sncf/osrd/stdcm/graph/STDCMPostProcessing.kt	66.66%	0 Missing and 1 partial ⚠️
...c/main/kotlin/fr/sncf/osrd/stdcm/graph/TimeData.kt	95.45%	0 Missing and 1 partial ⚠️

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Additional details and impacted files

@@             Coverage Diff              @@
##                dev    #8740      +/-   ##
============================================
- Coverage     37.03%   37.02%   -0.02%     
- Complexity     2208     2212       +4     
============================================
  Files          1255     1256       +1     
  Lines        113915   113997      +82     
  Branches       3188     3188              
============================================
+ Hits          42190    42205      +15     
- Misses        69830    69896      +66     
- Partials       1895     1896       +1     

Flag	Coverage Δ
core	74.79% <93.06%> (+0.04%)	⬆️
editoast	72.15% <ø> (-0.05%)	⬇️
front	14.95% <ø> (-0.02%)	⬇️
gateway	2.20% <ø> (ø)
osrdyne	2.71% <ø> (ø)
railjson_generator	87.49% <ø> (ø)
tests	86.37% <ø> (ø)

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[Erashin]

Looks good :)