Improve performance of route matching

While looking at some flamegraphs of API requests, I noticed several times that GrapePathHelpers::NamedRouteMatcher#route_match? was one of the methods with the highest durations.

It's not that bad all the time, but even on good runs it's still one of the top ones:

This method is used to generate API links, specially these _links that are always present in our responses:

This MR attempts to optimize this by stringifying the arguments only once.

This also improves the uses_segments_in_path_helper? check by using the memoized required_helper_segments in DecoratedRoute