refactor(protocol): improve base-fee math and remove L1 min base fee

[dantaik]

This PR is based on suggestions from OZ. See below.

Maxim: My feedback:

First and second points are resolved IMO About the third point, is your opinion that the base fee should not be allowed to go below 0,1 gwei on Taiko L2 ? If so, is there a reasoning behind this number ? It seems a bit arbitrary, for example I see that the last tx on Base has a < 0.1 gwei gas price (see below). My issue was that the computation was basefee(x) = 1/A * exp( x ), and you force basefee(x) >= 1 (1 wei). So I was saying that the multiplication by 1/A could be removed, that way it would naturally be bounded by 1 wei to the downside which would be simpler and would save precision in the exponential. If you want to bound it by C, you could do C * exp(x). To be clear it was a nitpick, you likely won't need this precision in practice, but it’s also a bit clearer (and what Ethereum is doing).

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Changes

• Removed the min base-fee design so now in theory, L2 base fee can be as small as 1 wei. We introduced the min base-fee design so that we can witness some changes in base fees on testnets, but maybe a arbitrary value for min base-fee is not a good idea and in practice, a base fee of 0.01 gwei is no different than a base fee of 1 wei for the rollup or our token holders.

• Also changed the base fee math of calculating the base fee from basefee(x) = 1/A * exp( x ) to basefee(x) = exp( x ). As said in the deleted comment in packages/protocol/contracts/L2/Lib1559Math.sol, the new math is equivalent to the previous one but offers better precision.

With a test, I can verify that:

• base fee will reach 0.01 gwei if gasExcess is greater than 130 x gasTargetPerL1Block
• base fee will reach 0.1 gwei if gasExcess is greater than 149 x gasTargetPerL1Block
• base fee will reach 1 gwei if gasExcess is greater than 167 x gasTargetPerL1Block
• base fee will reach 10 gwei if gasExcess is greater than 186 x gasTargetPerL1Block
• base fee will reach 100 gwei if gasExcess is greater than 204 x gasTargetPerL1Block

[openzeppelin-code[bot]]

refactor(protocol): improve base-fee math and remove L1 min base fee

Generated at commit: 3c430da5d6f637a36c359d89c10f7481da5a8876

🚨 Report Summary

	Severity Level	Results
Contracts	Critical High Medium Low Note Total	2 2 0 5 41 50
Dependencies	Critical High Medium Low Note Total	0 0 0 0 0 0

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