[DTP-951] Implement `LiveObjects.getRoot()` method

[VeskeR]

This PR is based on https://github.com/ably/ably-js/pull/1890, please review it first.

Tests for SYNC sequence are added in https://github.com/ably/ably-js/pull/1894.

Resolves DTP-951

Summary by CodeRabbit

• New Features

  • Introduced event-driven programming capabilities with the addition of EventEmitter and SyncCompleted event in the LiveObjects class, enhancing synchronization handling.

• Bug Fixes

  • Improved test suite for LiveObjects to ensure proper channel attachment before executing tests, leading to more reliable test outcomes.