feat(sidecar): make simple arb event-aware

[ming1523]

Updates tempo-sidecar simple-arb to avoid sweeping every pool on every loop.

This change keeps the existing fallback full rescan, but shifts the steady-state path to an event-aware dirty-pair workflow:

• track pool-affecting events
• enqueue dirty pairs
• rebalance only changed pools between full rescans
• expose basic dirty-pair/full-sweep metrics

The result is a cheaper and more production-like rebalancer without changing protocol behavior.

[github-actions]

This PR has been marked stale due to 7 days of inactivity.

[ming1523]

Reviving this lane. The PR is still awaiting the requested review from @Zygimantass, and there are no visible failing checks on the current head. Keeping it active instead of letting the stale marker speak for the current state.