AsyncClient raises a bare RuntimeError when middleware returns a sync-stream response #176

A middleware that short-circuits on an AsyncClient and returns a response built from a sync iterator makes the client raise a raw RuntimeError when it reads the body before decoding:

import asyncio

import httpx2
import httpware


async def short_circuit(request: httpx2.Request, next: object) -> httpx2.Response:
    return httpx2.Response(200, content=iter([b'{"a": 1}']), request=request)


async def main() -> None:
    async with httpware.AsyncClient(base_url="http://x", middleware=[short_circuit]) as client:
        await client.get("/", response_model=dict)


asyncio.run(main())
# RuntimeError: Attempted to call an async iterator on a sync stream.

The error comes from await response.aread() in AsyncClient before decoding. It is a programming error in the middleware, but it surfaces as a bare RuntimeError from inside httpx2 that doesn't point at the middleware. Options: raise a TypeError that names the problem, or accept a sync stream by reading it with read().