Feature request: add earliest_event_after() / latest_event_before() methods for DateEventSeries

[evansd]

I don't think we necessarily want to implement exactly this, but it's worth recording this kind of thing.

Original proposal was to be able to replace code like this:

dereg_date = (
    practice_registrations
    .where(practice_registrations.end_date.is_not_null())
    .where(practice_registrations.end_date.is_on_or_after(snapshot_date))
    .sort_by(practice_registrations.end_date)
    .first_for_patient()
    .end_date
)

With code like this:

dereg_date =  practice_registrations.end_date.earliest_event_after(snapshot_date)

But lots of useful discussion and other ideas in the Slack thread:
https://bennettoxford.slack.com/archives/C069YDR4NCA/p1737469592861429

[evansd]

Some related ideas also being kicked around in this Slack thread:
https://bennettoxford.slack.com/archives/C069YDR4NCA/p1732130446018819