Don't allow subclassing of AndroidCalendar anymore

[rfc2822]

Preparation for bitfireAT/davx5-ose#1552

[Copilot]

Pull Request Overview

This PR enforces that AndroidCalendar can no longer be subclassed by removing the factory interface and making it a final class, then updating all call sites and tests to instantiate AndroidCalendar directly.

• Eliminated AndroidCalendarFactory and factory parameters in AndroidCalendar methods.
• Changed AndroidCalendar from open to final and updated find/findByID to return AndroidCalendar.
• Refactored tests and helper classes (TestCalendar, test fixtures) to stop using subclasses.

Reviewed Changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
lib/src/main/kotlin/at/bitfire/synctools/test/InitCalendarProviderRule.kt	Removed AndroidCalendar.Factory argument in findByID call
lib/src/main/kotlin/at/bitfire/ical4android/AndroidEvent.kt	Dropped unused isOrganizer variable
lib/src/main/kotlin/at/bitfire/ical4android/AndroidCalendarFactory.kt	Deleted the factory interface file
lib/src/main/kotlin/at/bitfire/ical4android/AndroidCalendar.kt	Made class final; removed factory parameters and default factory
lib/src/androidTest/kotlin/at/bitfire/ical4android/impl/TestCalendar.kt	Converted subclass to a utility object returning AndroidCalendar
lib/src/androidTest/kotlin/at/bitfire/ical4android/AndroidEventTest.kt	Updated test calendar type and default parameters to AndroidCalendar
lib/src/androidTest/kotlin/at/bitfire/ical4android/AndroidCalendarTest.kt	Removed factory argument from findByID call

Comments suppressed due to low confidence (2)

lib/src/androidTest/kotlin/at/bitfire/ical4android/impl/TestCalendar.kt:16

• [nitpick] Consider renaming TestCalendar to something like TestCalendarHelper to reflect its role as a utility and avoid confusion with the previous subclass.

object TestCalendar {

lib/src/main/kotlin/at/bitfire/ical4android/AndroidCalendar.kt:249

• Consider using a MutableList (e.g., mutableListOf<AndroidCalendar>()) instead of LinkedList for better performance and memory characteristics, unless you specifically need linked-list behavior.

                val calendars = LinkedList<AndroidCalendar>()