chore(linter/prefer-array-flat-map): move category to performance

Author: camc314

crates/oxc_linter/src/rules/unicorn/prefer_array_flat_map.rs

@@ -39,7 +39,7 @@ declare_oxc_lint!(
     /// ```
     PreferArrayFlatMap,
     unicorn,
-    style,
+    perf,
     fix
 );