tests: add ETCS LoA (slowdown) tests on speed-space chart

[bougue-pe]

Add tests on the bending points of the speed-space chart for ETCS's LoA:

• mostly the start and end of braking
• also one more on the point where ETCS's Guidance curve stops being used in favor of Permitted Speed curve (~236 km/h)
  

Fixes #10495 (last test missing)

Note that safety speed and short slip speed may disappear for ETCS, but this will be a good occasion to check that it changes the tests.

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Codecov Report

Attention: Patch coverage is 86.04651% with 12 lines in your changes missing coverage. Please review.

Project coverage is 81.83%. Comparing base (3f83ed4) to head (acabf78).
Report is 10 commits behind head on dev.

Files with missing lines	Patch %	Lines
tests/tests/test_train_schedule.py	86.04%	12 Missing ⚠️

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Additional details and impacted files

@@            Coverage Diff             @@
##              dev   #10769      +/-   ##
==========================================
- Coverage   81.83%   81.83%   -0.01%     
==========================================
  Files        1081     1081              
  Lines      106882   106957      +75     
  Branches      729      721       -8     
==========================================
+ Hits        87469    87528      +59     
- Misses      19372    19388      +16     
  Partials       41       41              

Flag	Coverage Δ
editoast	74.31% <ø> (-0.02%)	⬇️
front	89.38% <ø> (-0.01%)	⬇️
gateway	2.18% <ø> (ø)
osrdyne	3.28% <ø> (ø)
railjson_generator	87.50% <ø> (ø)
tests	87.87% <86.04%> (-0.27%)	⬇️

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[Erashin]

Thanks for that!
By the way, #10565 might just modify these values, so whomever merges first wins? :p JK, let's keep ourselves updated ;)

EDIT: Should also fail if this pr is merged: #10768

[shenriotpro]

Thanks

[bougue-pe]

Well spotted @Erashin : I added a commit to fixup driver behavior change after rebase.