Implement network manager simulator lifecycle (#53)

crates/libremetaverse-types/src/compat.rs

@@ -466,8 +466,61 @@ impl Drop for CancellationRegistration {
     }
 }
 
-#[derive(Debug, Default, Eq, Hash, PartialEq)]
-pub struct Subscription;
+/// RAII guard for a mapped event subscription.
+///
+/// Dropping or explicitly closing the guard invokes the removal callback once.
+/// The callback normally owns only a weak reference to the event registry, so
+/// an abandoned subscription cannot keep its publisher alive.
+#[must_use = "dropping the subscription immediately unregisters the handler"]
+pub struct Subscription {
+    close: Option<Box<dyn FnOnce() + Send + Sync>>,
+}
+
+impl Subscription {
+    pub fn new(close: impl FnOnce() + Send + Sync + 'static) -> Self {
+        Self {
+            close: Some(Box::new(close)),
+        }
+    }
+
+    pub fn close(mut self) {
+        if let Some(close) = self.close.take() {
+            close();
+        }
+    }
+
+    #[must_use]
+    pub const fn is_active(&self) -> bool {
+        self.close.is_some()
+    }
+
+    pub const fn detached() -> Self {
+        Self { close: None }
+    }
+}
+
+impl Default for Subscription {
+    fn default() -> Self {
+        Self::detached()
+    }
+}
+
+impl fmt::Debug for Subscription {
+    fn fmt(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {
+        formatter
+            .debug_struct("Subscription")
+            .field("active", &self.is_active())
+            .finish()
+    }
+}
+
+impl Drop for Subscription {
+    fn drop(&mut self) {
+        if let Some(close) = self.close.take() {
+            close();
+        }
+    }
+}
 
 pub type EventHandler<T> = Arc<dyn Fn(T) + Send + Sync>;