--- Returns a new string with \`text\` inserted at position \`pos\` in \`str\`.
--- @param str string The original string.
--- @param pos number The position at which to insert \`text\` (1-based index).
--- @param text string The text to insert.
--- @return string The new string with \`text\` inserted at the specified position.
function string_insert(str: string, pos: number, text: string) end