Readable and Writable helpers for String, HashMap and HashSet (#4834)

* Add more read/write methods for string signals

* add helpers for HashMap and HashSet as well

* fix typo

* fix conflicting string and str extensions

* fix counters example

examples/07-fullstack/server_sent_events.rs

@@ -38,7 +38,7 @@ fn app() -> Element {
 
         // And then poll it for new events, adding them to our signal
         while let Some(Ok(event)) = stream.recv().await {
-            events.write().push(event);
+            events.push(event);
         }
 
         anyhow::Ok(())