TerraNexus Additions

🛣️ Road Height System

• Added 15 fixed road height variants ranging from 1/16 to 15/16.
• The existing asphalt_layer block is now reused as the fixed 1/16 height.
• The existing Asphalt Slab is integrated as the 8/16 (½ block) height.
• No duplicate blocks were created for the existing 1/16 and 8/16 variants.
• Added 13 new block variants for the missing intermediate heights.
• Roads no longer require stacking multiple layers to achieve different elevations.
• Added precise collision and selection boxes for every height variant.
• All height variants share the same asphalt texture and centralized material properties.
• Reused existing height models wherever possible.
• Removed redundant 8/16 and 16/16 models.
• Creative inventory now lists road height blocks in ascending order.
• Added blockstates, item definitions, loot tables, stonecutter recipes, tags, and translations for all variants.
• Introduced an extensible registration system using FixedRoadHeightBlock and ASPHALT_HEIGHTS.