Make `UniChanPath` worker more resilient to node going down

[romac]

Crate

relayer

Summary

Follow-up to #903

Problem Definition

The packet worker should retry to process an event batch to deal with nodes being unreachable for a short period of time.

Proposal

Add retry mechanism to packet worker.

Acceptance Criteria

The packet worker retries to process an event batch a few times before giving up.

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