Sessions per user

Split each user's events into sessions. A new session starts when an event comes more than 30 minutes after that user's previous event. A gap of exactly 30 minutes stays in the same session. The first event of a user always starts a session.

For every user with events, return:

• sessions, how many sessions they had
• avg_session_minutes, the average session length in minutes, where a session's length is the time from its first event to its last event (a session with one event is 0 minutes). Round to 1 decimal place.