feat(axum): expose hashed runtime asset path

Generate a SHA-256 content hash for the embedded hemx runtime, expose the hashed path from hemx-axum, serve immutable runtime headers, and update examples to load the hemx-owned path instead of fixed /hemx.js URLs.

req: axum_integration/005

hemx-axum/src/lib.rs

@@ -27,6 +27,16 @@ pub const fn runtime_js() -> RuntimeJs {
     RuntimeJs
 }
 
+// req: axum_integration/005
+pub const fn runtime_js_hash() -> &'static str {
+    hemx_js::RUNTIME_JS_HASH
+}
+
+// req: axum_integration/005
+pub const fn runtime_js_path() -> &'static str {
+    hemx_js::RUNTIME_JS_PATH
+}
+
 #[derive(Clone, Copy, Debug, Eq, PartialEq)]
 pub enum PageMode {
     Full,
@@ -1382,6 +1392,16 @@ impl IntoResponse for RuntimeJs {
             header::CACHE_CONTROL,
             HeaderValue::from_static("public, max-age=31536000, immutable"),
         );
+        response.headers_mut().insert(
+            header::ETAG,
+            HeaderValue::from_str(&format!("\"{}\"", runtime_js_hash()))
+                .expect("runtime hash is a valid ETag"),
+        );
+        response.headers_mut().insert(
+            header::CONTENT_LENGTH,
+            HeaderValue::from_str(hemx_js::RUNTIME_JS.len().to_string().as_str())
+                .expect("runtime length is a valid header value"),
+        );
         response
     }
 }
@@ -1390,6 +1410,14 @@ pub fn runtime_js_source() -> &'static str {
     hemx_js::RUNTIME_JS
 }
 
+pub fn runtime_js_script_src() -> &'static str {
+    runtime_js_path()
+}
+
+pub fn runtime_js_route_path() -> &'static str {
+    runtime_js_path()
+}
+
 // req: push/001, req: push/003, req: push/004
 pub fn sse<S, E>(batches: S) -> Sse<impl Stream<Item = Result<Event, E>> + Send>
 where