fix(core): Improve object merging (#11685)
* test: merge function test
* refactor: Improve object merging and type handling
- Enhance isObject function to strictly check for object types
- Refine merge function type signature for better TypeScript support
- Optimize deep merging logic for nested objects and arrays
- Ensure undefined values are properly handled during merge
* Update merge.test.ts
* Update merge.ts
---------
Co-authored-by: Balázs Orbán <info@balazsorban.com>
