refactor: use switch/case in parser, move options

- Replace if/else chains with switch/case in ical-parser
- Move CalendarSourceOptions to calendar-source.ts

Co-authored-by: Ona <no-reply@ona.com>

packages/aris-source-apple-calendar/src/calendar-source.ts

@@ -8,9 +8,15 @@ import type {
 	CalendarDAVClient,
 	CalendarEventData,
 	CalendarFeedItem,
-	CalendarSourceOptions,
 } from "./types.ts"
 
+export interface CalendarSourceOptions {
+	/** Number of additional days beyond today to fetch. Default: 0 (today only). */
+	lookAheadDays?: number
+	/** Optional DAVClient instance for testing. Uses tsdav DAVClient by default. */
+	davClient?: CalendarDAVClient
+}
+
 import { CalendarKey, type CalendarContext } from "./calendar-context.ts"
 import { parseICalEvents } from "./ical-parser.ts"