core: stdcm: rely on fixed point to compute final envelope

[eckter]

Fix #6981

We used to rely on the max speed envelope to run the final simulation and apply the standard allowance. With this change, we only rely on fixed time points to apply both standard and engineering allowances.

Includes a couple bugfixes:

1. When computing an allowance with ranges that don't add any time, we set the speed at the start/end of those ranges
2. BlockAvailabilityInterface.Unavailable.firstConflictOffset is now an Offset<TravelledPath>.

[codecov]

Codecov Report

Attention: Patch coverage is 89.70588% with 21 lines in your changes are missing coverage. Please review.

Project coverage is 29.00%. Comparing base (a6faf4c) to head (4e2837b).
Report is 3 commits behind head on dev.

Files	Patch %	Lines
.../sncf/osrd/stdcm/graph/PostProcessingSimulation.kt	88.75%	9 Missing and 10 partials ⚠️
...in/fr/sncf/osrd/stdcm/graph/STDCMPostProcessing.kt	95.00%	0 Missing and 1 partial ⚠️
.../preprocessing/implementation/BlockAvailability.kt	50.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##                dev    #7059      +/-   ##
============================================
+ Coverage     28.95%   29.00%   +0.04%     
- Complexity     2244     2250       +6     
============================================
  Files          1070     1070              
  Lines        132543   132627      +84     
  Branches       2713     2727      +14     
============================================
+ Hits          38379    38468      +89     
+ Misses        92587    92579       -8     
- Partials       1577     1580       +3     

Flag	Coverage Δ
core	80.09% <89.70%> (+0.28%)	⬆️
editoast	74.80% <ø> (-0.05%)	⬇️
front	9.29% <ø> (ø)
gateway	2.45% <ø> (ø)
railjson_generator	87.15% <ø> (ø)
tests	83.07% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[Erashin]

LGTM