Add an "expand-recurrences" boolean property (defaulting to TRUE) to both
GcalCalendarMonitor and GcalTimeline. When set to FALSE:
- Recurring master components are kept as single events without expanding
each recurrence instance.
- Detached recurrence instances are ignored.
- Pruning outside range retains recurring master events so they are not
prematurely removed.
- Subscriber filtering permits recurring master events within the
subscriber model.
This allows consumers like search providers to avoid expanding all recurrence
instances when searching, improving performance and avoiding duplicate hits.
Part-of: <https://gitlab.gnome.org/GNOME/gnome-calendar/-/merge_requests/808>
