chore: add #[non_exhaustive] to remaining public structs (#768)

* chore: add #[non_exhaustive] to remaining public structs

* chore: add #[non_exhaustive] to remaining public types

* chore: enable exhaustive_structs/enums clippy lints

* test: add untagged ServerResult deserialization regression tests

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

@@ -30,6 +30,7 @@ use crate::{
 };
 
 #[derive(Debug, Clone)]
+#[non_exhaustive]
 pub struct StreamableHttpServerConfig {
     /// The ping message duration for SSE connections.
     pub sse_keep_alive: Option<Duration>,
@@ -62,6 +63,33 @@ impl Default for StreamableHttpServerConfig {
     }
 }
 
+impl StreamableHttpServerConfig {
+    pub fn with_sse_keep_alive(mut self, duration: Option<Duration>) -> Self {
+        self.sse_keep_alive = duration;
+        self
+    }
+
+    pub fn with_sse_retry(mut self, duration: Option<Duration>) -> Self {
+        self.sse_retry = duration;
+        self
+    }
+
+    pub fn with_stateful_mode(mut self, stateful: bool) -> Self {
+        self.stateful_mode = stateful;
+        self
+    }
+
+    pub fn with_json_response(mut self, json_response: bool) -> Self {
+        self.json_response = json_response;
+        self
+    }
+
+    pub fn with_cancellation_token(mut self, token: CancellationToken) -> Self {
+        self.cancellation_token = token;
+        self
+    }
+}
+
 #[expect(
     clippy::result_large_err,
     reason = "BoxResponse is intentionally large; matches other handlers in this file"