Mark Task Continuity Messages as Oneway

Messages from `TaskContinuityManager` were getting rejected, since the transport wasn't set up to process them. This change amends the transport to do just that.

Test: Added unit tests
Bug: 400970610
Flag: android.companion.enable_task_continuity
Change-Id: I479cb0994e43ec5b77d2e1eaa3972496b5632ac2