Allow overriding prerender route rules

[pi0]

#1033 (comment)

Currently, we directly consume route rules in prerenderer to infer routes to prerender (https://github.com/unjs/nitro/blob/main/src/prerender.ts#L32)

We need to additionally create a radix3 instance that can actually match and merge route rules to handle overrides (for example prerender /news/** except /news/live with prerender: false)

[pi0]

Solving with #45 (i was wrong in above description)