Separated orchid-host and orchid-extension

This is an architectural change that allows me to implment specifics first and generalize along observed symmetries in orchid-base

orchid-base/src/msg.rs

@@ -0,0 +1,16 @@
+use std::io;
+
+pub fn send_msg(write: &mut impl io::Write, msg: &[u8]) -> io::Result<()> {
+  write.write_all(&(u32::try_from(msg.len()).unwrap()).to_be_bytes())?;
+  write.write_all(msg)?;
+  write.flush()
+}
+
+pub fn recv_msg(read: &mut impl io::Read) -> io::Result<Vec<u8>> {
+  let mut len = [0u8; 4];
+  read.read_exact(&mut len)?;
+  let len = u32::from_be_bytes(len);
+  let mut msg = vec![0u8; len as usize];
+  read.read_exact(&mut msg)?;
+  Ok(msg)
+}