✨ feat(error): add invalid message age error

- add `InvalidMessageAge` error variant to the `Error` enum
- include a message parameter to provide details about the invalid age

src/error.rs

@@ -48,4 +48,7 @@ pub enum Error {
     /// Error from config
     #[error(transparent)]
     Config(#[from] config::ConfigError),
+    /// Invalid message age specification
+    #[error("Invalid message age: {0}")]
+    InvalidMessageAge(String),
 }