feat(protocol): show my idea of reducing 1 sstore in libproving

[dantaik]

Currently each provingBlock tx have 6 sstore ops. This PR shows my idea to reduce it to almost 5.

The idea is that we only write stateRoot once every 32 blocks for cross-chain bridging synchronisation. This means when the ring-buffer is reused, we can use 4700 less gas, a ~2.5% reduction.

The downside of this change is that blockHash in events will not always be the block hash, sometimes it's the hash of blockhash and stateroot.

So is it worth it?

[openzeppelin-code]

feat(protocol): show my idea of reducing 1 sstore in libproving

Generated at commit: 131b140fa5b0ac050685ccaf79e53e242fbdce98

🚨 Report Summary

	Severity Level	Results
Contracts	Critical High Medium Low Note Total	2 2 0 8 42 54
Dependencies	Critical High Medium Low Note Total	0 0 0 0 0 0

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