* Introduced setup_pubsub_client for setting up a PubSub client and fetching queue item data. (#1088)

* Extracted queue-related logic into a new `queue_helpers` module for better organization.

* Refactored slot waiting logic into utility functions for reusable code in `epoch_manager` and `utils` modules.

* Get rid of most of unwraps in epoch_manager.

Author: sergeytimoshin