Make the function bounds for map less restrictive

packages/signals/src/signal.rs

@@ -257,7 +257,7 @@ impl<T: 'static> Signal<T> {
     }
 
     /// Map the signal to a new type.
-    pub fn map<O>(self, f: fn(&T) -> &O) -> SignalMap<O> {
+    pub fn map<O>(self, f: impl Fn(&T) -> &O + 'static) -> SignalMap<O> {
         SignalMap::new(self, f)
     }
 }