fix: body parsing function (#670)

crates/tuono_lib/tests/utils/post_api.rs

@@ -0,0 +1,12 @@
+use serde::Deserialize;
+use tuono_lib::Request;
+
+#[derive(Deserialize)]
+struct Payload {
+    data: String,
+}
+
+#[tuono_lib::api(POST)]
+async fn health_check(req: Request) -> String {
+    req.body::<Payload>().unwrap().data
+}