fix(processor): replace panic with graceful error in activePartitions

[sriman0707]

Description

Replaces a panic(err) call in processor.activePartitions() with graceful error handling.

Previously, when the database connection was temporarily lost, activePartitions() would panic. This panic terminated the runner's pinger goroutine, silently crashing the active event-processing loop.

With this change, the handler logs the connection error, records a metric, and returns an empty partition list. This allows the pinger loop to gracefully retry fetching active partitions on the next tick once the database recovers.

Linear Ticket

N/A (External Open Source Contribution)

Security

• The code changed/added as part of this pull request won't create any security issues with how the software is being used.

[contributor-support]

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