fix: properly handle FnOnce closure in onopen callback

Use Rc<RefCell<Option<>>> pattern to allow FnOnce closure to work with
FnMut requirement, fixing compilation error in River.

Author: sanity

rust/Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "freenet-stdlib"
-version = "0.1.21"
+version = "0.1.22"
 edition = "2021"
 rust-version = "1.71.1"
 publish = true

rust/src/client_api/browser.rs

@@ -88,8 +88,11 @@ impl WebApi {
         conn.set_onerror(Some(onerror_callback.as_ref().unchecked_ref()));
         onerror_callback.forget();
 
+        let onopen_handler = Rc::new(RefCell::new(Some(onopen_handler)));
         let onopen_callback = Closure::wrap(Box::new(move || {
-            onopen_handler();
+            if let Some(handler) = onopen_handler.borrow_mut().take() {
+                handler();
+            }
         }) as Box<dyn FnMut()>);
         // conn.add_event_listener_with_callback("open", onopen_callback.as_ref().unchecked_ref());
         conn.set_onopen(Some(onopen_callback.as_ref().unchecked_ref()));