Adding support for mixed basis during measurement

[akshaydaf]

Previously mixed bases such as:

@qpu
def with_phase_60() -> bit[2]:
    return '00' | {'0p', '0m', '1p', '1m'@60}.measure

and

@qpu
def no_phase() -> bit[2]:
    return '00' | {'0p', '0m', '1p', '1m'}.measure

were not working. This change introduces a factor_separable function, which takes in a BasisLiteral and returns a BasisTensor, that the existing lowering code already handles. Additionally, an update was made to the measure path to ignore phases.