mavcaldav: add comprehensive test suite (14 cases)
Covers:
- iCal parsing: filters today's events, excludes past/future/all-day
- VEVENT parsing: TZID, UTC, and all-day (nil) events
- DTSTART/DTEND parsing: UTC, local (treated as UTC), all-day, invalid
- safeKey sanitization: spaces→dashes, strip special chars
- writeIfChanged: no-prev writes, same-value skips, diff-value writes,
read-error and write-error propagation
- pollOnce end-to-end: httptest.Server + fakeCore verifies calendar_busy
+ calendar_event facts written with correct keys/values
kami
6daa96b66e