Sessionize user events
Your task
Sessionize a stream of user events. Input is a list of (user, ts) tuples already sorted by ts ascending overall, plus an integer 'gap'. For each user independently, consecutive events belong to the same session if the difference between an event's ts and the previous event's ts (for that user) is <= gap; a larger difference starts a new session. Return a list of (user, session_count) tuples for every user that appears, sorted by user ascending. The input may be empty. A user with a single event has 1 session.
Examples
count_sessions(events: list[tuple], gap: int) -> list[tuple]Example 1
Input
count_sessions([["a", 1], ["a", 3], ["a", 10], ["b", 2]], 5)Output
[["a", 2], ["b", 1]]