fix: speedup slow matching of static routes

[marvinhagemeister]

This PR speeds up matching static file routes. Previously, each static file route would get their own URLPattern instance which is slow and we loose the fact that we could do an exact match by doing so.

What this PR does is extend the type of a route pattern to be URLPattern | string. When it's a string than we treat it as being an exact match and sidestep the whole cost of doing a URL parse + regex match. Note that only we ourselves can create string-based patterns. User supplied patterns are always parsed into URLPattern like before.

Thanks to @jviide for the idea of adding caching for static routes 👍

In some real world sites I've tested this fix with this reduces route matching cost from 62ms -> 0.7ms

Fixes #1931