Given a list of strings, group the strings so that each group contains words that are anagrams of each other. Discuss both a sorting-based signature and a frequency-vector signature. Return the groups in any order. Function signature: ```python def group_anagrams(words: list[str]) -> list[list[str]]: pass ``` Constraints: - All strings contain lowercase English letters unless the interviewer adds a broader character set. - Words may repeat. - The order of groups and words within a group does not matter. - Analyze the cost of sorting each word versus building a frequency signature. Examples: ```text words = ['eat', 'tea', 'tan', 'ate', 'nat', 'bat'] Output may be [['eat','tea','ate'], ['tan','nat'], ['bat']] ```