Sleep to go faster

The problem was I was basically flushing twice for every message when
doing request reply.
This gives the sender the opportunity to finish writing a full message
to the queue, which we then check for before flushing.

This makes request reply latency benchmarks go down from like 90ms to
200us.

src/Server/Client.zig

@@ -40,6 +40,16 @@ pub fn start(self: *Client, io: std.Io) !void {
     std.debug.assert(self.to_client.end == 0);
     while (true) {
         self.to_client.end = try self.recv_queue.get(io, self.to_client.buffer, 1);
+        // Wait 1 nanosecond to see if more data is in the queue.
+        // If there is, add it to the write buffer before sending it.
+        // The reason for this is because if we send the first chunk as soon as we get it,
+        // we will likely be sending a partial message, which will end up being way slower.
+        try io.sleep(.fromNanoseconds(1), .awake);
+        self.to_client.end += try self.recv_queue.get(
+            io,
+            self.to_client.buffer[self.to_client.end..],
+            0,
+        );
         try self.to_client.flush();
     }
 }