feat: add local feature for !Send tool handler support (#740)

* feat: add local feature for !Send tool handler support

* fix: gate streamable HTTP transport on not(local) feature

crates/rmcp/src/transport/streamable_http_server/session.rs

@@ -33,7 +33,7 @@ pub mod never;
 
 /// Controls how MCP sessions are created, validated, and closed.
 ///
-/// The [`StreamableHttpService`](super::StreamableHttpService) calls into this
+/// The `StreamableHttpService` calls into this
 /// trait for every HTTP request that carries (or should carry) a session ID.
 ///
 /// See the [module-level docs](self) for background on sessions.

crates/rmcp/src/transport/streamable_http_server/tower.rs

@@ -204,7 +204,7 @@ impl<S, M> Clone for StreamableHttpService<S, M> {
 impl<RequestBody, S, M> tower_service::Service<Request<RequestBody>> for StreamableHttpService<S, M>
 where
     RequestBody: Body + Send + 'static,
-    S: crate::Service<RoleServer>,
+    S: crate::Service<RoleServer> + Send + 'static,
     M: SessionManager,
     RequestBody::Error: Display,
     RequestBody::Data: Send + 'static,