feat!: add MRTR behavior support (SEP-2322) (#929)

* feat!: add MRTR behavior support

* feat: harden SEP-2322 MRTR support

* ci: diff public API only on features common to base and head

cargo public-api builds both revisions with the same feature set, so a
feature introduced (or removed) by a PR broke the build of the other
revision. Restrict the all-features diff to features present in both the
base and head revisions.

crates/rmcp-macros/src/prompt_handler.rs

@@ -35,7 +35,7 @@ pub fn prompt_handler(attr: TokenStream, input: TokenStream) -> syn::Result<Toke
             &self,
             request: rmcp::model::GetPromptRequestParams,
             context: rmcp::service::RequestContext<rmcp::RoleServer>,
-        ) -> Result<rmcp::model::GetPromptResult, rmcp::ErrorData> {
+        ) -> Result<rmcp::model::GetPromptResponse, rmcp::ErrorData> {
             let prompt_context = rmcp::handler::server::prompt::PromptContext::new(
                 self,
                 request.name,