YUNG's Rarer Structures - exact structure-set overrides

This datapack overrides the matching YUNG's structure-set resources.
It preserves each mod's original structure list, salt, placement type, and
exclusion settings, changing only spacing and separation to:

spacing: 1000
separation: 700

Important: Minecraft does not have a generic structure-set "priority" JSON
field. The override works by using the exact same namespace/path as the mod's
resource. Put this datapack in the world's datapacks folder.

These changes affect newly generated terrain/chunks; already-generated chunks
will not be retroactively rearranged.
