feat: add title field for data types (#410)

* feat(model): add title field to various structs

* fix(test): fix test json schema

* fix(model): allow boxed type  in `ts_union` macro

examples/servers/src/sampling_stdio.rs

@@ -105,6 +105,7 @@ impl ServerHandler for SamplingDemoServer {
         Ok(ListToolsResult {
             tools: vec![Tool {
                 name: "ask_llm".into(),
+                title: None,
                 description: Some("Ask a question to the LLM through sampling".into()),
                 input_schema: Arc::new(
                     serde_json::from_value(serde_json::json!({