perf(server): offload sync disk/db IO to tokio blocking thread pool

Makes apply_sync_write, write_to_local_delta, and store modify truly async, preventing the mcp-memory-server from locking the tokio executor during disk IO

server/src/handlers.rs

@@ -146,7 +146,7 @@ impl MemoryHandler {
                                     }
                                 }
                             }
-                        });
+                        }).await;
                         Ok(vec!["Entities created".to_string()][0].clone())
                     }
                     "create_relations" => {
@@ -172,7 +172,7 @@ impl MemoryHandler {
                                     }
                                 }
                             }
-                        });
+                        }).await;
                         Ok(vec!["Relations created".to_string()][0].clone())
                     }
                     "add_observations" => {
@@ -214,7 +214,7 @@ impl MemoryHandler {
                                     g.entities.insert(o.entity_name, e);
                                 }
                             }
-                        });
+                        }).await;
                         Ok(vec!["Observations added".to_string()][0].clone())
                     }
                     "delete_entities" => {
@@ -235,7 +235,7 @@ impl MemoryHandler {
                             master.relations.retain(|r| {
                                 !to_delete.contains(&r.from) && !to_delete.contains(&r.to)
                             });
-                        });
+                        }).await;
                         Ok(vec!["Entities deleted".to_string()][0].clone())
                     }
                     "delete_observations" => {
@@ -266,7 +266,7 @@ impl MemoryHandler {
                                     e.observations.retain(|o| !to_rem.contains(o));
                                 }
                             }
-                        });
+                        }).await;
                         Ok(vec!["Observations deleted".to_string()][0].clone())
                     }
                     "delete_relations" => {
@@ -299,7 +299,7 @@ impl MemoryHandler {
                                     r.from, r.to, r.relation_type, r.namespace
                                 ))
                             });
-                        });
+                        }).await;
                         Ok(vec!["Relations deleted".to_string()][0].clone())
                     }
                     "read_graph" => {
@@ -526,7 +526,7 @@ impl MemoryHandler {
                             if let Some(e) = master.entities.get_mut(&req.entity_name) {
                                 e.observations = req.summarized_observations;
                             }
-                        });
+                        }).await;
                         Ok(vec!["Entity condensed".to_string()][0].clone())
                     }
                     "add_task" => {
@@ -763,7 +763,7 @@ impl MemoryHandler {
                                 }
                             }
                             master.relations = MemoryState::unique_items(master.relations.clone());
-                        });
+                        }).await;
                         Ok(vec!["Entities merged".to_string()][0].clone())
                     }
                     "find_orphans" => {