Classical simulation doesn't work for registers with non-empty shape and dtype != QUInt

[tanujkhattar]

The following sample code fails with an error:

import attrs
from qualtran import QInt, Bloq, Signature, Register

@attrs.frozen
class TestMultiDimensionalReg(Bloq):
    n: int

    @property
    def signature(self):
        return Signature([Register('x', QInt(32), shape=(self.n,))])


    def on_classical_vals(self, x):
        print(x)
        return {'x': x}

bloq = TestMultiDimensionalReg(10)
bloq.call_classically(x=[-1] * 10)

Issue is due to hardcoded casts to unsiged types np.uints in

Qualtran/qualtran/simulation/classical_sim.py

Lines 47 to 56 in db8b993

	if reg.bitsize <= 8:
	dtype: Type = np.uint8
	elif reg.bitsize <= 16:
	dtype = np.uint16
	elif reg.bitsize <= 32:
	dtype = np.uint32
	elif reg.bitsize <= 64:
	dtype = np.uint64
	else:
	raise NotImplementedError(

[mpharrigan]

I suspect those casts harken back to the time when there weren't data types and the classical simulation only did unsigned integers. This is used to initialize a multidimensional numpy array to contain the values. The data type of this numpy array should probably delegate to the QDType