writeTo
Receives channel provided by the engine and writes all data to it
Writes the content body directly to the given stream, bypassing the ByteWriteChannel intermediary.
Engine implementations that have access to a native blocking OutputStream (e.g. servlet engines backed by a thread-per-request model) should call this method instead of writeTo(ByteWriteChannel) to avoid dispatching to kotlinx.coroutines.Dispatchers.IO and the runBlocking bridge inside ByteWriteChannel.toOutputStream.
The caller is responsible for closing the stream after this method returns.