core: the block generator does not ensure routes are bounded by appropriate signals

[multun]

What happened?

In the real world, only some signals can be used to end / start routes. These signal cannot be passed when closed due to interlocking (Nf signals in french signaling).

Currently, we let block delimiting signals start and end routes, regardless of whether they can actually signal for the end of a route.

What did you expect to happen?

We should check whether signals at the end / start of routes are actually belong there, and raise a warning if they don't.

In practice, the is_route_delimiter property is missing from the current implementation.

How can we reproduce it (as minimally and precisely as possible)?

1. Create a route which ends with a non-route delimiting signal
2. No warning whatsoever

What operating system, browser and environment are you using?

• Browser: Firefox v109
• OS: Nixos v22.11
• Env: Local

OSRD version (top right corner Account button > Informations)

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