feat(axum): start stateful interactions tersely

Add state_interactions as a small helper for app-owned stateful registries, and use it in the workout exemplar to remove one layer of repetitive route wiring without hiding generated handles or app handlers.

req: axum_integration/003

req: ceremony/001

req: dx/003

req: codegen/002

req: examples/001

hemx-axum/src/lib.rs

@@ -460,6 +460,14 @@ pub const fn interactions(fingerprint: BuildFingerprint) -> HandlerRegistry {
     HandlerRegistry::new(fingerprint)
 }
 
+pub fn state_interactions<S>(fingerprint: BuildFingerprint, state: S) -> StateHandlerRegistry<S>
+where
+    S: Clone + Send + Sync + 'static,
+{
+    // req: axum_integration/003 req: ceremony/001
+    interactions(fingerprint).with_state(state)
+}
+
 impl InteractionRequest {
     pub fn dispatch(
         self,