bun: declare the endpoints in Bun.serve routes instead of branching on req.url

[nigrosimone]

Bun.serve has had a routes option since 1.2.3 and this entry runs 1.4, but it does not use it: fetch receives everything and the handler branches on req.url with a chain of ifs. This declares the endpoints in routes instead, so the router matches method and path and fills in req.params. fetch stays as the 404.

I should say where this comes from, because it looks bad otherwise. I wrote that first implementation myself in #1163 on 15 August, when completeness did not exist and not using the router cost nothing. Completeness arrived on 21 August in #1223 and the entry has carried routing: false since, which is an accurate description of my code and takes 2.5% off its composite, about 23 points on the published numbers. So a choice that was free when I made it now costs points to a framework that competes with mine, and I would rather fix it than leave it there to be read as me having favoured my own entry.

It is not a trade. Measured locally on the baseline shape with bun 1.3.14, alternating rounds: the chain of ifs 2,812 req/s, routes 2,832. The router is free here, so the 2.5% is a straight gain.

Every endpoint answers what it answered before, checked request by request against the previous build: the three baseline shapes, json with and without gzip, upload, static with identity and br, the missing file, the traversal guard, async-db, fortunes and the four crud verbs. One difference, on a method nobody sends: DELETE /baseline11 now gets 404 rather than being answered as a GET. Neither validate.sh nor the profile sends it.

completeness.routing goes to true with it.

Ref #1283