--- Strips a set of characters from the beginning and end of a string.
---
--- @param str string The string to strip.
--- @param chars string? The characters to strip. Defaults to whitespace characters (" \t\n\r").
--- @return string The stripped string.
--- @return number The index of the last character in the stripped string.
function string_strip(str: string, chars: string?) -> (string, number) end