feat: add Number of Different Integers in a String (#2595)

[Smithech]

Solve “Number of Different Integers in a String” #2595

Add the function diff_integers_in_string(phrase: str) -> int

• This function iterates through a string, checks whether each character is a digit, and keeps track of unique integers found in the string. It returns the total number of different integers.
• Documentation for the function has been added.

Example:

diff_integers_in_string("2595") # returns 3