Add comprehensive tests for z.date() handling including e2e OpenAPI tests

Co-authored-by: BenLorantfy <4398635+BenLorantfy@users.noreply.github.com>

Author: Copilot

packages/nestjs-zod/src/__e2e_tests__/openapi.test.ts

@@ -1,6 +1,8 @@
-export function assert(condition: unknown, message: string = 'Assertion failed'): asserts condition {
-    if (!condition) {
-        throw new Error(`[nestjs-zod] ${message}`);
-    }
+export function assert(
+  condition: unknown,
+  message = 'Assertion failed'
+): asserts condition {
+  if (!condition) {
+    throw new Error(`[nestjs-zod] ${message}`)
+  }
 }
-