feat(base-formula): add logic functions

packages/base-formula/src/functions/logic.ts

@@ -0,0 +1,12 @@
+// packages/base-formula/src/functions/logic.ts
+import { register } from "./registry";
+
+register({
+  name: "empty",
+  arity: { min: 1, max: 1 },
+  paramTypes: "any",
+  returnType: "boolean",
+  eval: ([v]) => v == null || v === "" || (typeof v === "object" && v !== null && "__err" in v),
+  doc: "Returns true if the value is null or empty string or an error.",
+  category: "logic",
+});