fix :handle mixed string and interger types in add()

[prsai0110]

Problem

simple_math.add() was not handling mixed types correctly and was concatenating values.

Solution

Added a type check to raise TypeError if arguments are not int or float.

Testing

Tested with both integer and mixed types — confirmed expected behavior.

[prsai0110]

I found a bug in the add() function where it doesn’t properly handle mixed string and integer types.
Instead of raising an error, it concatenates the values, producing incorrect output.

Steps to Reproduce

1. Run this code:

import simple_math
result = simple_math.add("5", 10)
print(result)