refactor: implement local barrier manager as event handler

[wenym1]

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What's changed and what's your intention?

Previously, we implement our local barrier manager as a struct shared by Arc<Mutex<LocalBarrierManager>>. In this PR, we implement the local barrier manager as a worker loop spawned as tokio task, and all original operations on it will be sent as worker events. In this way, there will be less contention between actors, and it is better for the implementation of partial checkpoint that will report the barrier progress in a finer granularity.

Some refactors are done accordingly.

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[BugenZhao]

LGTM!