[jtx rewrite] Add Handlers for Recurrence Fields

[ArnyminerZ]

Purpose

Copied from bitfireAT/synctools#410

Short description

• Implement RecurrenceFieldsHandler
• Implement tests for the new class

Checklist

• The PR has a proper title, description and label.
• I have self-reviewed the PR.
• I have added documentation to complex functions and functions that can be used by other modules.
• I have added reasonable tests or consciously decided to not add tests.

[Copilot]

Pull request overview

Adds recurrence-field support to the new JTX mapping pipeline by introducing a dedicated RecurrenceFieldsHandler, wiring it into JtxObjectHandler, and covering the behavior with unit tests (including a regression case for “RDATE-only recurrence”).

Changes:

• Implement RecurrenceFieldsHandler to map RRULE, RDATE, EXDATE, and exception RECURRENCE-ID.
• Update JtxObjectHandler to treat RDATE as recurrence so exceptions are included even without an RRULE.
• Add/extend Robolectric tests for both the new handler and exception-inclusion behavior.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 2 comments.

File	Description
synctools/src/main/kotlin/at/bitfire/synctools/mapping/jtx/JtxObjectHandler.kt	Registers the new handler and includes exceptions for RRULE or RDATE recurrence.
synctools/src/main/kotlin/at/bitfire/synctools/mapping/jtx/handler/RecurrenceFieldsHandler.kt	New handler mapping recurrence-related fields from JTX entities to ical4j properties.
synctools/src/test/kotlin/at/bitfire/synctools/mapping/jtx/JtxObjectHandlerTest.kt	Adds regression tests ensuring exceptions are included for RDATE-only recurrence.
synctools/src/test/kotlin/at/bitfire/synctools/mapping/jtx/handler/RecurrenceFieldsHandlerTest.kt	New test suite validating recurrence field mapping across timezone/all-day/floating cases.

[Copilot]

Pull request overview

Copilot reviewed 4 out of 4 changed files in this pull request and generated no new comments.