Number formatting function with digit grouping

It is necessary to implement a function that takes an integer and returns a string where the number is broken down into its digits with their respective weights.

Example of the function:

• input: 12
• output: "10 + 2"

Output format: each digit value (descriptor) is connected with a "+" sign with spaces on both sides. If the number consists of a single digit, the string containing only the number without a plus sign is returned.

The function should be written so that it correctly handles any non-negative integers, including zero.