## Description 

This PR introduces `ProgressSavingPolicy` to deal with two problems:
1. The current implementation has a bug on Sui side - checkpoints data
arrive out-of-order (e.g. checkpoint 10 may be processed earlier than
checkpoint 9), so existing `save_process` may cause us to miss blocks.
2. In current implementation we need to write progress to DB for every
call to `save_process`. This can be optimized to cache progresses in
memory and flush them periodically or conditionally.

We add two types of `ProgressSavingPolicy`, `SaveAfterDuration` and
`OutOfOrderSaveAfterDuration`:
* `SaveAfterDuration` only flushes the progress to DB after a period of
time
* `OutOfOrderSaveAfterDuration` assumes the data is out of order, and
will only write height N when it makes sure everything before N has been
received.
* 

## Test plan 

unit tests and production deployment.

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- [ ] Protocol: 
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