fix(rsc): await handler to avoid unhandled rejection

[hi-ogawa]

Description

• Related chore(rsc): debug rsc-html-stream uncaught enqueue error #573

@mjackson/node-fetch-server's request handler is typed as void, but internally it can reject when response stream is broken for whatever reason (e.g. when ReadableStream/TransformStream's transform, flush, pull, etc... throws).
https://github.com/mjackson/remix-the-web/blob/b5aa2ae24558f5d926af576482caf6e9b35461dc/packages/node-fetch-server/src/lib/request-listener.ts#L87

I was comparing with @hono/node-server (which is currently used by Waku) and this one swallows any stream errors internally, so the same won't happen. https://github.com/honojs/node-server/blob/cb52c36d1d5d5b68416c807ce4b231c8bc549e29/src/utils.ts#L20-L28. This difference might somehow affects this issue wakujs/waku#1521.

---

Okay, this is likely irrelevant for Waku.

I cannot reproduce any crash externally, but this can happen if there's a "bug" in stream handling e.g.

    responseStream = responseStream.pipeThrough(
      new TransformStream({
        flush() {
          throw new Error("boom")
        }
      }),
    );

⚠️⚠️⚠️ unhandledRejection ⚠️⚠️⚠️ Error: boom
    at Object.flush (/home/hiroshi/code/others/vite-plugin-react/packages/plugin-rsc/src/extra/ssr.tsx:50:17)
    at invokePromiseCallback (node:internal/webstreams/util:172:10)
    at Object.<anonymous> (node:internal/webstreams/util:177:23)
    at transformStreamDefaultSinkCloseAlgorithm (node:internal/webstreams/transformstream:621:43)
    at node:internal/webstreams/transformstream:379:11
    at writableStreamDefaultControllerProcessClose (node:internal/webstreams/writablestream:1162:28)
    at writableStreamDefaultControllerAdvanceQueueIfNeeded (node:internal/webstreams/writablestream:1251:5)
    at writableStreamDefaultControllerClose (node:internal/webstreams/writablestream:1218:3)
    at writableStreamClose (node:internal/webstreams/writablestream:722:3)
    at writableStreamDefaultWriterClose (node:internal/webstreams/writablestream:1091:10)

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commit: 9a5b687