Add overload proc macro for #[splat] function overloading

[Ajay-singh1]

This is a proof of concept for the overload! macro that makes #[splat]
easier to use for function overloading.

What it does

Case 1: Functions with single argument

overload! {
    fn foo(x: i32) { println!("i32: {}", x); }
    fn foo(x: f64) { println!("f64: {}", x); }
    fn foo(x: bool) { println!("bool: {}", x); }
}

foo(30);
foo(22.90);
foo(true);

Case 2: Functions with multiple arguments

overload! {
    fn foo(x: i32, y: f64) { println!("i32: {}, f64: {}", x, y); }
    fn foo(x: bool, y: i32, z: f64) { println!("bool: {}, i32: {}, f64: {}", x, y, z); }
}

foo(54, 63.90);
foo(true, 98, 65.09);

Current status

• Multiple functions: done
• Single argument: done
• Multiple arguments with mixed types: done
• Return values: in progress
• Methods: not started
• Generics: not started

Next steps

• Handle return values
• Handle methods
• Handle generics

[teor2345]

Let's fix and merge what we have now, then open other PRs for further changes?

[Ajay-singh1]

Done! We can merge this now , we can open other PRs for next changes.