maths/number_of_digits.py is naive!

[vasugamdha]

maths/number_of_digits.py has a naive method. The suggested method has a time complexity of O(n). We can count number of digits of a number in O(1).

[cclauss]

Can we put both algorithms into the same file and add a benchmark that proves that the theoretical performance improvement is achieved and that the proposed algorithm is noticeably faster than the current algorithm?

[vasugamdha]

@cclauss Yes! I have proposed the algorithm that is noticeably faster as num_digits_fast() in the #2221
Please review it. Thanks.