Optimize handlers to avoid deep clones of KnowledgeGraph, and fix database write concurrency issues

server/src/state.rs

@@ -49,6 +49,13 @@ impl MemoryState {
         self.graph.read()
     }
 
+    pub fn read_graph<F, R>(&self, f: F) -> R
+    where
+        F: FnOnce(&KnowledgeGraph) -> R,
+    {
+        self.graph.read_with(f)
+    }
+
     pub fn modify_graph<F: FnOnce(&mut KnowledgeGraph)>(&self, update_fn: F) {
         self.graph.modify(update_fn);
     }