refactor: move firmware workspace under firmware

firmware/libs/kaptan-config-derive/tests/ui.rs

@@ -0,0 +1,6 @@
+#[test]
+fn rejects_malformed_field_validation_attributes() {
+    let cases = trybuild::TestCases::new();
+    cases.compile_fail("tests/ui/*.rs");
+    cases.pass("tests/pass/*.rs");
+}