New BufferedSocket class (#8977)

* New BufferedSocket class

I'm starting to push Okio's socket throughout OkHttp,
and it turns out what I usually want is a BufferedSocket
instead.

* Flush not emit

* Track exception messages

* Use flush more

okhttp-testing-support/src/main/kotlin/okhttp3/internal/duplex/MockSocketHandler.kt

@@ -21,25 +21,13 @@ import java.util.concurrent.FutureTask
 import java.util.concurrent.LinkedBlockingQueue
 import java.util.concurrent.TimeUnit
 import mockwebserver3.SocketHandler
-import okio.BufferedSink
-import okio.BufferedSource
+import okhttp3.internal.connection.BufferedSocket
+import okhttp3.internal.connection.asBufferedSocket
 import okio.Socket
-import okio.buffer
 import okio.utf8Size
 
 private typealias Action = (BufferedSocket) -> Unit
 
-private class BufferedSocket(
-  val socket: Socket,
-) {
-  val source: BufferedSource = socket.source.buffer()
-  val sink: BufferedSink = socket.sink.buffer()
-
-  fun cancel() {
-    socket.cancel()
-  }
-}
-
 /**
  * A scriptable request/response conversation. Create the script by calling methods like
  * [receiveRequest] in the sequence they are run.
@@ -104,7 +92,7 @@ class MockSocketHandler : SocketHandler {
   }
 
   override fun handle(socket: Socket) {
-    val task = serviceSocketTask(BufferedSocket(socket))
+    val task = serviceSocketTask(socket.asBufferedSocket())
     results.add(task)
     task.run()
   }