Six declarations spell a byte buffer as bare `Buffer` / `Uint8Array`. Without
its type argument that widens to `ArrayBufferLike`, which also admits
`SharedArrayBuffer` — so the value is rejected at every Web API boundary it is
actually passed to: `BodyInit` for `new Response(...)` and `BlobPart` for
`new Blob([...])`.
Every one of them is already ArrayBuffer-backed at runtime. `hexToBytes()`
allocates with `new Uint8Array(len)`; `synthesizeGtts()` and `pcmToWav()` return
`Buffer.concat(...)`; `fetchRemoteImage()` returns
`Buffer.from(await response.arrayBuffer())`; `readPageResponseBody()` returns
`Buffer.from(body)`, which copies. The declarations were simply less specific
than the values, so this states what the code already guarantees.
Same fix#8533 applied to the multipart and gRPC-web bodies.
Fixes 5 of the 208 `tsc -p open-sse/tsconfig.json` diagnostics with no new ones:
3 in audioSpeech.ts (MiniMax hex, gTTS, Vertex Gemini TTS), 1 in
imageGeneration.ts (Topaz Blob upload) and 1 in browserBackedChat.ts.
Refs #8484
