style: update valid_input to use Python 3.12 type parameters

Applied PEP 695 syntax to the valid_input function by moving the 'num' generic into brackets. This resolves the UP047 error in the machine_learning directory.

Author: kvadrik

machine_learning/linear_discriminant_analysis.py

@@ -252,7 +252,7 @@ def accuracy(actual_y: list, predicted_y: list) -> float:
 num = TypeVar("num")
 
 
-def valid_input(
+def valid_input[num](
     input_type: Callable[[object], num],  # Usually float or int
     input_msg: str,
     err_msg: str,