Given an array of characters `chars`, compress it using the following algorithm:

Begin with an empty string `s`. For each group of consecutive repeating characters in `chars`:

- If the group's length is `1`, append the character to `s`.
- Otherwise, append the character followed by the group's length.

The compressed string `s` should not be returned separately, but instead, be stored in the input character array `chars`. Note that group lengths that are `10` or longer will be split into multiple characters in `chars`.

After you are done modifying the input array, return the new length of the array.

You must write an algorithm that uses only constant extra space.

Example 1:

    Input: chars = ["a","a","b","b","c","c","c"]
    Output: Return 6, and the first 6 characters of the input array should be: ["a","2","b","2","c","3"]
    Explanation: The groups are "aa", "bb", and "ccc". This compresses to "a2b2c3".

Example 2:

    Input: chars = ["a"]
    Output: Return 1, and the first character of the input array should be: ["a"]
    Explanation: The only group is "a", which remains uncompressed since it's a single character.

Example 3:

    Input: chars = ["a","b","b","b","b","b","b","b","b","b","b","b","b"]
    Output: Return 4, and the first 4 characters of the input array should be: ["a","b","1","2"].
    Explanation: The groups are "a" and "bbbbbbbbbbbb". This compresses to "ab12".

Constraints:

- `1 <= chars.length <= 2000`
- `chars[i]` is a lowercase English letter, uppercase English letter, digit, or symbol.