Handles processing of commands for a specific instance.

The InstanceProcessor is responsible for fetching, processing, and updating the status of commands belonging to a single instance. It is started dynamically by the InstanceMonitor when there are queued commands to process.

Responsibilities

• Fetch pending, failed, or timed-out commands for the assigned instance.
• Process each command and update its status in the database.
• Handle retries and error cases according to command queue logic.
• Ensure only one processor runs per instance at a time (enforced via Registry).

This module is typically supervised under the InstanceSupervisor as a dynamic child.