memory_links: return typed Vec<LinkInfo> with node weights

- hippocampus::memory_links now returns Vec<LinkInfo> with key,
  link_strength, and node_weight for each neighbor
- Unified memory_tool! macro: mut/ref as token, single main rule
- All tools use serde serialize/deserialize for RPC consistency
- jsonargs handlers now work in client mode (RPC to daemon)
- cli/graph.rs formats LinkInfo for display

Co-Authored-By: Proof of Concept <poc@bcachefs.org>

src/cli/graph.rs

@@ -28,9 +28,12 @@ pub async fn cmd_link(key: &[String]) -> Result<(), String> {
         return Err("link requires a key".into());
     }
     let key = key.join(" ");
-    let result = memory::memory_links(None, &key).await
+    let links = memory::memory_links(None, &key).await
         .map_err(|e| e.to_string())?;
-    print!("{}", result);
+    println!("Neighbors of '{}':", key);
+    for link in links {
+        println!("  ({:.2}) {} [w={:.2}]", link.link_strength, link.key, link.node_weight);
+    }
     Ok(())
 }