chore: gatekeeper fix race condition in Mongo DB

[Bushstar]

• Resolve: Fix race condition in Gatekeeper Mongo DB #1023

[Copilot]

Pull Request Overview

This PR fixes race conditions in the MongoDB implementation of the gatekeeper database by replacing multiple operations with atomic MongoDB operations.

• Replaces the setEvents method's delete-then-add pattern with a single atomic $set operation
• Updates clearQueue to use MongoDB's atomic $pull operation instead of read-modify-write pattern
• Adds consistent type usage with the QueueDoc interface

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