Stalwart 1.0 returns recurrence overrides as RFC 8984 PatchObjects, with
keys like participants/p1/participationStatus and nulls that remove.
Browser expansion spread them onto the occurrence, so a declined
occurrence stayed accepted and the pointer keys became junk properties.
Moved or resized occurrences also kept the time and length the rule
gave them and were placed by their original date.
Overrides are now applied as patches, occurrence times come from the
patched start, time zone and duration, and new changes merge into an
existing override without keys that are prefixes of one another.
