Faster Greedy Mesher

I took a shot at speeding up the `greedy` mesher. Have put it in `voxels.meshers.greedier` rather than replacing `greedy`.

Also included a basic benchmark - hope it helps :)

Before:
```
└─ greedy: 183.45ms
  └─ Hill: 23.503ms
  └─ Valley: 23.727ms
  └─ Hilly Terrain: 24.266ms
  └─ Checker: 26.520ms
  └─ Noise: 27.835ms
  └─ Sphere: 28.049ms
  └─ Dense Noise: 29.556ms
```
After:
```
└─ greedier: 76.608ms
  └─ Hill: 10.123ms
  └─ Valley: 10.169ms
  └─ Noise: 10.749ms
  └─ Dense Noise: 10.843ms
  └─ Checker: 11.296ms
  └─ Hilly Terrain: 11.318ms
  └─ Sphere: 12.106ms
```