Use Vec for PathRouter

[pickfire]

Routes in path seemed to work with linear memory instead of needing the extra hash and tracking of prev_route_id, a Vec should work just fine while having the benefits of cache locality.

Motivation

Vec seemed to be able to fulfill routes without needing HashMap, as well as better cache locality.

Solution

Change PathRouter to use Vec.

[mladedav]

Thanks, this looks good as it might simplify things though I would be surprised if cache locality played any measurable role here as HashMaps are also backed by a single allocation and I would be surprised if the interleaved u32s made much difference. Plus it's iterated over in just a few scenarios.