Delay emitter until NiceGUI-level handshake done (#4754)

This PR fix #4753, possibly paves the way to shifting the Socket.IO
intialization earlier.

Notable changes: 

- [Handshake is done only when receiver server
ok](https://github.com/zauberzeug/nicegui/commit/793adb4814b382c755749289f9583fc90e0b24dd)
- [Retry emitting message repeatedly until handshake is
done](https://github.com/zauberzeug/nicegui/commit/a107315d1d117bd5ab5ce130a10e968c33532157)

Old logic: 
- Handshake is done when we sent the message. Who cares how long that
message may take to reach the server
- If the handshake is not done, we wait 10ms and emit regardless. 
- Meaning if the handshake is not done after 10ms, the message gets
lost.

New logic: 
- We wait for the NiceGUI side to return True before considering the
handshake is done
- If the handshake is not done, we keep on retrying at 10ms interval
- Meaning if the handshake is not done after 10ms, the message does not
get lost.

About the handshakes: 

- Engine.IO-level handshake, receiving `0{sid: "m-Lwo1fStO8e-QAbAAAU",
upgrades: [] ...`
- Socket.IO-level handshake, receiving
`40{"sid":"oxVbOYM32Hieu1anAAAV"}`
- Some components wait for this handshake to emit, because they need
`window.socket.id`, like Leaflet
- NiceGUI-level handshake, sending `420["handshake", {client_id:
"7b6b9df6-e24a-489c-9dd2-012a08b34a10"...` and receiving `430[true]`
- This PR refers to waiting for this handshake, as it is the most
important one.
- Before this handshake, any event emitted will not be registered, since
the Socket.IO ID is not associated with the `client_id` yet.

nicegui/static/nicegui.js

@@ -191,7 +191,7 @@ function renderRecursively(elements, id) {
           });
         const delayed_emitter = () => {
           if (window.did_handshake) emitter();
-          else setTimeout(emitter, 10);
+          else setTimeout(delayed_emitter, 10);
         };
         throttle(delayed_emitter, event.throttle, event.leading_events, event.trailing_events, event.listener_id);
         if (element.props["loopback"] === False && event.type == "update:modelValue") {
@@ -358,9 +358,9 @@ function createApp(elements, options) {
               console.log("reloading because handshake failed for clientId " + window.clientId);
               window.location.reload();
             }
+            window.did_handshake = true;
             document.getElementById("popup").ariaHidden = true;
           });
-          window.did_handshake = true;
         },
         connect_error: (err) => {
           if (err.message == "timeout") {