Closures in Rust are anonymous functions that can capture variables from their environment. They are similar to functions but have some unique properties that make them powerful and flexible. Closures are often used for short, simple operations and can be defined in a very concise way.

A closure is defined using a pair of vertical bars | that enclose the parameters, followed by the closure body. Here's a simple example of a closure that adds two numbers:

let add = |a: i32, b: i32| a + b;

In this example, add is a closure that takes two parameters, a and b, and returns their sum. You can call this closure just like a function:

let result = add(2, 3); // result is 5

Closures can capture variables from their enclosing scope. For example:

let x = 2;
let add_x = |a: i32| a + x;
let result = add_x(3); // result is 5

In this case, the closure add_x captures the variable x from the surrounding scope and adds it to its parameter a.

Your task is to complete the implementation of the following closures:

• add_closure: This closure should return the sum of two integers.
• subtract_closure: This closure should return the difference between two integers.
• multiply_closure: This closure should return the product of two integers.

• Each closure should take two parameters of type i32.
• Each closure should return a result of type i32.

assert_eq!(add_closure(3, 4), 7);
assert_eq!(subtract_closure(10, 4), 6);
assert_eq!(multiply_closure(3, 5), 15);

• Remember to use the let keyword to define closures.
• Use the |a, b| syntax to define the parameters of the closure.