added a cacheFunction

[abdelrahman146]

The cacheFunction method takes a function and its parameters and adds it value in the cacheMap and return its value. if the passed cacheKey and the parameters are already cached. then it will not run the function again instead it will jus return the cached value. if the parameters values have changed then it will create another cache in the cache map.

Example:

    const sum = (...nums: number[]) => nums.reduce((total, curr) => total + curr, 0);
    let result = cache.cacheFunction('sum', sum, [1, 2, 3]);
    expect(result).toBe(6);
    result = cache.cacheFunction('sum', sum, [3, 4, 5]);
    expect(result).toBe(12);