Jit block machine

[chriseth]

Experimental code that resembles rust code auto-generated from constraints.

Next steps:

1. see what the performance impact of introducing proper fixed machine lookups has
2. see if we can auto-generate the assignments from the constraints - first in an abstract form
3. see if we can turn this abstract form either into rust or into pil.

Numbers on 1.:
It takes between 400-800ns to fill a full block using the lookups.