Refactor classical_sim.py bitwise functions to allow for signed values

[fpapa250]

bits_to_ints() and ints_to_bits() only work for conversions of unsigned integers. This limits the classical simulation correctness for bloqs using Join() because its on_classical_vals() implementation uses these functions. Therefore when we get the classical simulation of a bloq that uses Join() it cannot represent signed integers so we can't have tests for classical simulation of signed integer representations.

Currently this affects the signed implementation of Add() and doesn't allow us to classically simulate SimpleAddConstant(). Once this functionality has been changed we need to add tests for the classical simulation of the signed version of SimpleAddConstant().

[fdmalone]

in general I think we want a type_to_bits and bits_to_type method which will appropriately dispatch based on the type of the register. For fixed point we can probably write a little python implementation to define operations given some limited precision. #446

[fpapa250]

For tracking purposes: Also an issue for comparison of negative integers in the GreaterThan() bloq.