Add newtype wrappers for `StateGas` and `RegularGas`

We should do something like:

```python
from typing import NewType

StateGas = NewType(Uint)
RegularGas = NewType(Uint)

class StateGasPerByte(Uint):
    @overload
    def __mul__(self, other: Uint) -> StateGas:
        ...
```

So we don't mix up state-gas with regular-gas.