DEEP Iron Furnaces

Adds DEEP furnace variants for the Iron Furnaces mod.

| Furnace Tier | Fuel Yield | Speed | Block IDs |
|————–|————|——-|———–|
| Lead | 50 | 200 | 1676,1677 |
| Silver | 150 | 100 | 1678,1679 |
| Amethyst | 75 | 400 | 1680,1681 |

Note: Fuel Yield here is in terms of items smelt per fuel used, not in terms of time burning per fuel used

Known bugs and issues
None so far :3