Add a Progressive Coal Upgrade Path (Crushed Coal & Coke)

Coal currently lacks a gradual fuel-quality upgrade path compared to other systems in COI.
Oil-based fuels already follow a clear progression (Diesel → Gas → Hydrogen), and iron ore can be crushed to improve metallurgical efficiency.

By contrast, coal jumps directly from raw fuel to late-game graphite, which feels like a large technological leap.

I suggest adding a progressive coal processing chain focused on efficiency:

Raw Coal – basic fuel
Crushed Coal – preprocessing to improve efficiency or reduce consumption（This could also reuse existing crusher logic, similar to iron ore）
Coke – advanced solid fuel optimized for high-temperature and metallurgical use

This would smooth coal’s mid-game progression, improve consistency with existing design philosophy, and keep all steps optional and trade-off based. Graphite would remain a late-game material upgrade rather than a direct jump.