Update lcu_util to allow user to specify sub_bit_precision

[kjm538]

Can preprocess_lcu_coefficients_for_reversible_sampling be updated to allow the user to input epsilon or sub_bit_precision? Sometimes it is preferable to specify the number of precision bits explicitly.

[fdmalone]

I don't see why not. In the notebooks I believe we often set epsilon to be $2^{-n_b}$ directly, but it might be a bit more convenient to make this an optional input too.

[tanujkhattar]

@Vicara12 Can you take a look?