Accept `Sequence` instead of `List`

[jangop]

This is minor, I know. tokenize simply iterates over texts, so in addition to list, tuple is fine. The intended type hint for this is Sequence.

I am not sure which version of Python this project targets, but judging from the other type hints in this file, I am going to assume <3.9. Otherwise, I would suggest importing Sequence from collections.abc instead of typing.