meta: stdcm: possible performance improvements

[eckter]

• core: stdcm: we may need a better way to identify visited edges (in space) #6273
• core: stdcm: find a better way to identify visited edges (in time) #8268
• core: spacing resources: we require the path to be one block longer than necessary #7788
• core: improve Conflicts.checkSpacingRequirements in stdcm context #7650
• editoast: stdcm: pre-filter train requirements that can't affect the new train #7649
• core: stdcm: further improve heuristic #7642
• core: stdcm: improve the way we check engineering allowance possibility #7136

#6273 is more complex than the rest, but it would lead to the largest performance improvements if we can fix the issue. It probably depends on #7642 and #7582.

The other issues don't really have any particular ordering or dependency.

There's also #7200 which isn't strictly related to stdcm, but we sometimes run pathfinding requests as preprocessing. It could also be used to speed up the stdcm heuristic preprocessing by a little bit.