Release 3cc0868

Refactor tile setting in map.gd to include default z-index

- Updated set_cell calls in set_tile and sync_tile functions to include a default z-index of 0, ensuring consistent tile placement.
- Maintained existing logic for checking tile existence and alternative coordinates, preserving robustness in tile management.
- Improved clarity of comments to reflect changes in tile setting behavior and the importance of z-index in tile rendering.