[dtypes] Update the NumericalFormatter to use the learn_rounding_digits from RDT

[R-Palazzo]

Problem Description

Like other RDT transformers, the NumericalFormatter has to learn the rounding digits of the column it is transforming. Every RDT transformer that does this uses the utility method learn_rounding_digits.

Expected behavior

Remove this method:

SDV/sdv/data_processing/numerical_formatter.py

Line 55 in a0e0a76

def _learn_rounding_digits(data):

Replace its call by calling learn_rounding_digits from RDT

Additional context

After this change and when Issue 2156, RDT Issue 858, RDT Issue 855 are closed, sampling should work on SDV with the new pandas dtype on every python version.