Adding Mean and MeanBy

[usman1100]

Title: Add Mean and MeanBy functions for ints and floats

Issue: #412

Description:

This PR adds two new functions to the math library:

• Mean: Calculates the mean of a collection of numbers.
• MeanBy: Calculates the mean of a collection of numbers using a provided iteratee function.

These functions are implemented using generics to support both integers and floats. They do not cater to complex types, as the concept of a mean for complex numbers can be misleading and requires specialized handling.

Thorough unit tests have been included to ensure the correctness of the functions.

Code Changes:

• Added two functions in math.go
• Added tests for the two functions in math_test.go

Testing:

All tests pass successfully.

Reviewers, please provide any feedback or questions you may have.

[usman1100]

@samber Awaiting your review