Informational Audit Recommendations

[ZenGround0]

These are the best practices recommendations coming out of the composable audit

1. Remove unused errors OnlyRailParticipantAllowed and FeeWithdrawalNativeTransferFailed from Errors.sol
2. Use custom errors instead of revert strings. In particular RateChangeQueue is where we are doing this.
3. Clear serviceFeeParticipant from rail struct when zeroing out rail -- I believe this one actually has some state usage impact since FVM is smart enough to release KAMT slots that point at zero values and we are not correctly zeroing out rail struct values as we intended
4. Update solidity version to 0.8.33 -- Im not sure the state of FEVM support but I think we should be mostly current thanks to filb's work

5. Update the NatSpec comment at L1144 to correctly identify the caller as payer.

These are all items we should address whenever we deploy a new version.