Support reading from ReadCursor / writing to WriteCursor via Socket

[armanbilge]

There are some really efficient APIs for this:

• https://man7.org/linux/man-pages/man2/sendfile.2.html
• https://docs.oracle.com/javase/8/docs/api/java/nio/channels/FileChannel.html#transferTo-long-long-java.nio.channels.WritableByteChannel-
• https://docs.oracle.com/javase/8/docs/api/java/nio/channels/FileChannel.html#transferFrom-java.nio.channels.ReadableByteChannel-long-long-
• https://std.in/using-sendfile-with-nodejs/

I'm fairly confident we can add a default implementation to Socket just using the Stream APIs. If so, then this opens the door for more specialized overrides on the actual implementation.