fix: resolve clippy warnings across workspace (#1195)

* fix: resolve clippy warnings across workspace

* ci: also run clippy on rmcp with all features except local

--all-features enables the local feature, which cfg-gates out
tower.rs and most of the test suite, so the existing clippy step
never actually lints them.

examples/clients/src/sampling_stdio.rs

@@ -1,3 +1,8 @@
+#![expect(
+    deprecated,
+    reason = "This example demonstrates the deprecated MCP sampling API"
+)]
+
 use anyhow::Result;
 use rmcp::{
     ClientHandler, ServiceExt,