String Compression

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.