multilayer ijump astar optimization: if start and goal are on different layers, the first via should be 0 cost

[seveibar]

Currently, when a via is placed astar chooses to go back and look for ways to do the route without a via, wasting iterations. This is obvious if you lower the via cost.

There's no reason to go back if at least one via is required on the path

For plated holes or multi-layer goals, this isn't relevant

[homie-gg]

Here are some pull requests that might be helpful reference for this task:

• Orthogonal Intersection Optimal Hops (ijump enhancement)
• ijump-max (ijump v2) algorithm, enhancements to logging, refactor infinite grid autorouter
• Multilayer traces and vias, fixes traces routed inside Trace.ts are always routed on top layer