Magnitude and Squared Magnitude helpers
vertex_tree_search_segment(): Search for vertexes that exist on an edge

Signature:
  * `vertex_node_t *vertex_tree_search_segment(vertex_node_t *tree, float3 start, float3 end);`

Does not return vertex identies, instead a fresh tree of values.
index_walk_edges(): Like edge_tree_walk() but callbacks get the index