Add C++ implementation for composite k case in `Finding Power of Factorial Divisor` article

Description

The article explains the algorithm for handling composite k in the "Finding Power of Factorial Divisor" problem, but it does not provide a complete C++ reference implementation.

It would be helpful to include a function that:

• Prime-factorizes k.
• Uses fact_pow() to compute the exponent of each prime factor in n!.
• Returns the minimum exponent after accounting for each factor's multiplicity.

Adding this implementation would make the article more practical and consistent with other cp-algorithms articles that include complete reference code.