feat(core) RequestRule (#9489)

## Summary
Instead of trying to derive the prefix_rule for a command mechanically,
let's let the model decide for us.

## Testing
- [x] tested locally

codex-rs/execpolicy/src/rule.rs

@@ -96,6 +96,8 @@ pub trait Rule: Any + Debug + Send + Sync {
     fn program(&self) -> &str;
 
     fn matches(&self, cmd: &[String]) -> Option<RuleMatch>;
+
+    fn as_any(&self) -> &dyn Any;
 }
 
 pub type RuleRef = Arc<dyn Rule>;
@@ -114,6 +116,10 @@ impl Rule for PrefixRule {
                 justification: self.justification.clone(),
             })
     }
+
+    fn as_any(&self) -> &dyn Any {
+        self
+    }
 }
 
 /// Count how many rules match each provided example and error if any example is unmatched.