ReminderOverride.Minutes now carries a List<Int> of lead times so a target
can hold several reminders at once; an app that offers a single reminder uses a
one-element list. Map helpers move to Map<Long, List<Int>> (empty list = explicit
None), and the codec gains a third (list) separator while single legacy values
round-trip byte-identically. Adds reminderOverrideForMinutes/normalizeReminders/
reminderLeadsFor. Upstreamed from Calendula's per-calendar multi-reminders.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Jean-Luc Makiola
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