Trace development route preparation (#96453)
## Summary
This PR introduces the first bounded route-preparation phases used by
Request Insights. It instruments existing matcher and bundler boundaries
without changing their behavior or making the spans default-public
OpenTelemetry data.
- trace development route matching and route preparation while a route
is ensured
- keep production matcher reload as a separate sibling phase so reload
work is not charged to matching
- surface the internal phases as `match route`, `prepare route`, and
`reload route matchers` in Request Insights
- cover cold and warm page, App Route/API, and dynamic-route behavior in
both development bundlers
- preserve the existing matcher results, errors, and public OTel
allowlist
## Verification
- `pnpm test-dev-turbo
test/development/app-dir/request-insights-route-preparation/request-insights-route-preparation.test.ts`
- `pnpm test-dev-webpack
test/development/app-dir/request-insights-route-preparation/request-insights-route-preparation.test.ts`
- `pnpm --filter=next types`
