refactor: flush logic

[joelsmith-2019]

Overview

This PR refactors the flush mechanisms for both noble and ethereum-based chains. Flushes will no longer look back a lookbackPeriod all the way up until the chain tip. There will now be a minimum gap of lookbackPeriod between the last flushed block and the chain tip. This ensures that transactions currently being processed will not get picked up again via the flush.

New flush logic

First Flush
startBlock = currentHeight - (2 * lookbackPeriod)
finishBlock = currentHeight - lookbackPeriod

Genesis                        Start      Finish      Tip
|--------------------------------|----------|----------|

Subsequent Flushes
startBlock = last flushed block
finishBlock = currentHeight - lookbackPeriod

Genesis                                   Start      Finish      Tip
|-------------------------------------------|----------|----------|

Note: StartBlock corresponds to which block the flush should start on. FinishBlock corresponds to which block the flush should end on. There will always be a gap of lookbackPeriod between tip and finish.

How to Configure

For best results and coverage, the lookback period in blocks should correspond to the flush interval. If a chain produces 1 block a second and the flush interval is set to 30 minutes (1800 seconds), the lookback period should be at least 1800 blocks. When in doubt, round up and add a small buffer.

Examples

Consider a 30 minute flush interval (1800 seconds)

• Ethereum: 12 second blocks = (1800 / 12) = 150 blocks
• Polygon: 2 second blocks = (1800 / 2) = 900 blocks
• Arbitrum: 0.26 second blocks = (1800 / 0.26) = ~6950 blocks

[joelsmith-2019]

Still need to update the README.md.

[Reecepbcups]

LGTM, thanks for the call on this. helped clear up my questions re: circle <-> relayer check flows

[jtieri]

this is a nice refactor, I really like the updates to the docs/comments as well