writeTimeoutMillis not active during RequestBody.writeTo

[yschimke]

@swankjesse I tried to implement this using

            .socketFactory(
              DelayingSocketFactory(onWrite = {
                Thread.sleep(100L)
              }),

But if I break point at Thread.sleep, then socket.sink().timeout().timeoutNanos() is always cleared (0).

I suspect a bug with write timeout, but this replicates a timeout just by checking if we have the bad timeout value.

Originally posted by @yschimke in #9108