Train slot search module

This module handles the search for solutions.

To summarize how it works: the search space is defined as one large decision tree.

We first build one decision tree that lists all possible paths, where each “decision” is the direction taken. We then build another tree on top of it that handles simulations and conflicts, branching is done when the new train gets to choose if it goes before or after a different train.

We then run an A* on the resulting graph.