refactor(rules:if): throw on unsupported node type in _nodeToAtom

Replaces the silent `return ""` default with an explicit error, making
unexpected AST node types fail loudly instead of producing a wrong result.

Author: ticapix

src/utils.ts

@@ -230,7 +230,7 @@ export class Utils {
                 const n = node as jsep.BinaryExpression;
                 return `${Utils._nodeToAtom(n.left)} ${n.operator} ${Utils._nodeToAtom(n.right)}`;
             }
-            default: return "";
+            default: throw new Error(`Unsupported expression node type: ${(node as any).type}`);
         }
     }