migrate 392 questions to pattern format

backend/data/questions/longest-valid-parentheses.yaml

@@ -8,8 +8,10 @@ categories:
   - stack
   - dynamic-programming
 patterns:
-  - dynamic-programming
-  - monotonic-stack
+  - slug: dynamic-programming
+    is_optimal: false
+  - slug: monotonic-stack
+    is_optimal: true
 
 function_signature: "def longest_valid_parentheses(s: str) -> int:"