Skip walking all tokens when loading range suppressions (#22446)
- Adds `Tokens::split_at()` to get tokens before/after an offset.
- Updates `Suppressions::load_from_tokens` to take an `Indexer` and use
comment ranges to minimize the need for walking tokens looking for
indent/dedent.
Adapted from
https://github.com/astral-sh/ruff/pull/21441#pullrequestreview-3503773083
Fixes #22087
