Implement native VivoxTest validation (#95)

crates/libremetaverse/src/network_manager.rs

@@ -1265,6 +1265,17 @@ impl Simulator {
             .map(|inner| Caps::native_from_inner(inner, self.native_clone_without_caps()))
     }
 
+    /// Looks up one capability without exposing the simulator's mutable caps state.
+    ///
+    /// Capability URLs are bearer credentials. Callers must not log or persist
+    /// the returned URI.
+    pub fn native_capability_uri(&self, capability: &str) -> Result<Option<Uri>, Error> {
+        let Some(caps) = self.native_caps() else {
+            return Ok(None);
+        };
+        caps.capability_uri(capability.to_owned())
+    }
+
     pub(crate) fn native_id(&self) -> UUID {
         self.data.id
     }