[Handoff][9/N] Cache PackageMetadata when Serializing

This change adds a cache for package metadata retrieved from PackageManager, so we don't have to serialize each time we send a message.

Flag: android.companion.enable_task_continuity
Bug: 400970610
Test: Added Unit Testing
Change-Id: If4a61c022a61c300a331d69a8eeac1c059aad52a