Fix: expand REPORT leaves recurrence properties on expanded instances

_strip_single_event() removed the recurrence-defining properties (RRULE,
EXDATE, EXRULE, RDATE) with a single try/except around sequential
delattr() calls. When one of them was absent (e.g. an event with no
EXDATE), the AttributeError aborted the whole block and the following
properties -- notably RDATE -- were left on the expanded
single-occurrence VEVENTs returned by a calendar-data expand REPORT.

Remove each property independently so a missing one no longer prevents
removal of the others. Add a regression test and fixture.

Co-Authored-By: Claude <noreply@anthropic.com>

radicale/tests/static/event_rrule_rdate.ics

@@ -0,0 +1,12 @@
+BEGIN:VCALENDAR
+VERSION:2.0
+PRODID:-//Radicale tests//NONSGML test//EN
+BEGIN:VEVENT
+UID:event_rrule_rdate
+DTSTART:20060102T170000Z
+DURATION:PT1H
+RRULE:FREQ=DAILY;COUNT=3
+RDATE:20060110T170000Z
+SUMMARY:Daily recurring meeting
+END:VEVENT
+END:VCALENDAR