Add sort before groupby

[denini08]

Hello!

While reading the code and running some tests, I noticed a small detail that could cause unexpected behavior when the input list is not ordered. The itertools.groupby() function assumes the data is already sorted by the key (docs), but in _group_by_match_index this was not guaranteed.

So I added a sorted() call before the groupby() to make the behavior safe and consistent, regardless of the input order.

Interestingly, the rest of the codebase already follows this same pattern:

• rules.py:300 - Uses sorted() before groupby()
• match.py:62 - Maintains proper ordering
• match.py:71 - Maintains proper ordering

I also added a small test that explicitly checks the behavior with unsorted input data, just to make sure this case is always covered.

Thank youfor the project!
I hope this improvement is helpful.