core: remove neutral section hacks to improve reliability

[multun]

The current implementation of neutral ranges has at least two troublesome hacks:

• when leaving a neutral section, the train takes time to start drawing power again.
  due to the design of the current implementation, this time is converted into an
  approximate distance
• power is cut ahead of time using an announce zone, instead of having the driver
  react to the signal. this zone is there regardless of routes

These hacks bring about several bugs:

• the length of neutral section is extended by an approximation of the distance
  required to start drawing power again. This approximation is always too high
  if the train is slowing down. If the train is slowing down to a stop, it can
  get stuck in this approximated extension. This issue will vanish once this
  gets simulated over time instead.
• if a train stops inside the neutral section announce zone, it has to start
  drawing power anyway to start back up, then cut power in the neutral section.
  this behavior is very hard to emulate with the current simulation engine.
• if a sign announces a neutral section just before a switch, the announce zone
  is directional. getting this right probably means treating annonce signs as
  signals, and treat those as route dependant. This is a lot of work, and needs
  to wait until trains can react to signals (train sim v3).

These hacks were a bad idea in the first place, and the features they were meant
to implement will be a lot easier to implement once trains:

• are simulated in a causal way
• can react to signals

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 29.44%. Comparing base (6079b64) to head (be21975).
Report is 6 commits behind head on dev.

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Additional details and impacted files

@@              Coverage Diff              @@
##                dev    #7413       +/-   ##
=============================================
+ Coverage     18.79%   29.44%   +10.64%     
+ Complexity     2016     2012        -4     
=============================================
  Files           903     1162      +259     
  Lines        114916   143499    +28583     
  Branches       2809     2808        -1     
=============================================
+ Hits          21594    42247    +20653     
- Misses        91668    99594     +7926     
- Partials       1654     1658        +4     

Flag	Coverage Δ
core	76.24% <100.00%> (-0.05%)	⬇️
editoast	72.31% <ø> (?)
front	9.83% <ø> (ø)
gateway	2.41% <ø> (-0.03%)	⬇️
railjson_generator	87.49% <ø> (ø)
tests	83.96% <ø> (ø)

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[bloussou]

Thanks a lot 🧹