Add comments and fix tests

Also added networkBytesAsValue and restored bytesAsValue.
These are useful for treating the bytes from the network directly as a Message.
Otherwise, the init function would overwrite the packet type and length to be correct.
I would like the message handling to fail if the message body is incorrect.

src/Client.zig

@@ -127,7 +127,7 @@ pub fn connect(payload: []const u8, allocator: Allocator) !?SaprusConnection {
     const len = try sock.receive(&response_buf);
 
     std.debug.print("response bytes: {x}\n", .{response_buf[0..len]});
-    initial_conn_res = SaprusMessage.init(.connection, response_buf[0..len]);
+    initial_conn_res = try .networkBytesAsValue(response_buf[0..len]);
 
     // Complete handshake after awaiting response
     try broadcastSaprusMessage(msg, randomPort());