Add http.serve() API based on Fetch (Request -> Response)

### What is the problem this feature will solve? Node provides `fetch`, `Request/Response`, and Web Streams, but no high level server API using this model. Other runtimes such as [Deno](https://docs.deno.com/api/deno/~/Deno.serve) and [Bun](https://bun.com/reference/bun/serve) expose a `serve` API based on the Fetch contract. In Node, similar patterns are commonly implemented in userland (e.g., frameworks like [Hono](https://hono.dev/)), which indicates demand for this abstraction. This was discussed in #42529 and received support, however that issue is focused on `request.toWeb()`, so opening a separate issue focused on this API. ### What is the feature you are proposing to solve the problem? Add a high-level `http.serve(handler)` API. An example shape could be: ```ts http.serve((req) => new Response("ok")) handler: (Request) => Response | Promise<Response> ``` This would coexist with the existing `http.createServer`, and be a high level alternative using WHATWG APIs instead. ### What alternatives have you considered? - Continue using `http.createServer` directly. - Implement this in userland, or use existing 3rd party solutions.