feat(kms): add operation timeout and typed retry policy engine (#5472)

crates/kms/src/lib.rs

@@ -71,6 +71,10 @@ pub mod config;
 mod encryption;
 mod error;
 pub mod manager;
+// The executor is wired into the Vault backends in a follow-up change; until
+// then the module is only exercised by its own tests.
+#[allow(dead_code)]
+mod policy;
 pub mod service;
 pub mod service_manager;
 mod time_serde;