fix: Use public Zod v4 .def API, fix CSV coercion and merge clone

- Use schema.def (public API) instead of _zod?.def ?? _def in getSchemaDefault
- Fix CSV array coercion being dropped by restructuring control flow
- Replace structuredClone with recursive deepMerge clone for Jest compat
- Update test for maintenanceKey now being optional per schema change

Author: dblythy

spec/Options/schemas/schemas.spec.js

@@ -39,7 +39,6 @@ describe('ParseServerOptionsSchema', () => {
     const paths = result.error.issues.map(i => i.path[0]);
     expect(paths).toContain('appId');
     expect(paths).toContain('masterKey');
-    expect(paths).toContain('maintenanceKey');
     expect(paths).toContain('serverURL');
   });
 

src/Options/loaders/mergeConfig.ts

@@ -52,7 +52,9 @@ function deepMerge(
         sourceVal as Record<string, unknown>
       );
     } else if (isPlainObject(sourceVal)) {
-      target[key] = structuredClone(sourceVal);
+      const clone: Record<string, unknown> = {};
+      deepMerge(clone, sourceVal as Record<string, unknown>);
+      target[key] = clone;
     } else {
       target[key] = sourceVal;
     }