Reads and parses the head of an HTTP/1.x request straight off an [`AsyncRead`] source, with zero copies of the parsed fields. Bytes are streamed into the caller-owned `data` buffer until the `CRLFCRLF` head terminator is seen (or the peer hangs up). The returned [`RawRequest1x`] then borrows directly from `data` — the method, url, version, header block and already-buffered body are all sub-slices
source not stored for this graph (policy: none)
nothing calls this directly
no outgoing calls
no test coverage detected