Add iCalDAV Kotlin library to CalDAV libraries

[one-kash]

Summary

This PR adds iCalDAV to the list of CalDAV libraries.

About iCalDAV

iCalDAV is a Kotlin CalDAV client library published on Maven Central under the org.onekash group. Key features include:

• RFC 5545 compliant iCalendar parsing and generation (VEVENT, VTODO, VJOURNAL)
• CalDAV client with automatic server discovery
• WebDAV ACL support (RFC 3744)
• Recurring events with full RRULE/RDATE/EXDATE expansion
• Sync engine with offline support and conflict resolution
• Android module for CalendarContract integration
• Tested with iCloud, Nextcloud, Radicale, and Baikal servers

Links

• GitHub: https://github.com/iCalDAV/iCalDAV
• Maven Central: https://central.sonatype.com/namespace/org.onekash
• License: Apache 2.0