Refactor Cursor handle management to eliminate leaks and support per-zoom handles

- Removed the dedicated `handle` field from Cursor; all native handles are now stored in `zoomLevelToHandle`.
- Extracted OS handle creation logic from constructors into a lazy-loading mechanism triggered by `win32_getHandle`.
- Ensured the default zoom level (100) handle is always created during cursor construction.
- Updated hashCode, equals, isDisposed, and destroy to work with zoom-level handles.
- Prevents resource leaks caused by undisposed temporary cursors and supports safe, reusable handle management across zoom levels.

Author: ShahzaibIbrahim