Investigate Eiger Fan Ignoring Stream Tasks

If the Eiger Fan doesn't receive new task from the eiger's stream in a couple of days, it seems to ignore any new tasks, even though it looks healthy. It seems as if the connection to the stream queue become stale if left alone.

The current attempt to fix this is in this [branch](https://github.com/DiamondLightSource/eiger-detector/tree/add_fan_restart), which wraps the process in a loop to enable a `restart`. However, the actual reason for this behavior should be investigate.

Start by reviewing the add_fan_restart branch and the Eiger Fan's stream-queue consumer entry point. Reproduce the failure after leaving the stream idle for several days, then trace why new tasks are ignored. Done means the stale-connection cause is identified and a verified fix or focused follow-up is documented.

Written by the indexing model from the issue text.