Feat: reject invalid keys

packages/core/tests/kitchen_sink.rs

@@ -6,7 +6,7 @@ fn basic_syntax_is_a_template() -> Element {
     let var = 123;
 
     rsx! {
-        div { key: "12345", class: "asd", class: "{asd}", class: if true {
+        div { key: "{asd}", class: "asd", class: "{asd}", class: if true {
                 "{asd}"
             }, class: if false {
                 "{asd}"