MixBytes: add user op max cost setter

[fedealconada]

As per MixBytes recommendation, adds a userOpMaxCost setter.
Also adds some polishes.

[github-actions]

Slither report

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Summary

[rrecuero]

I would set the initial value here because sponsor paymaster is already initialized so the initializer is not going to be called

[fedealconada]

we can't do that when using UUPS...
https://docs.openzeppelin.com/upgrades-plugins/1.x/writing-upgradeable#avoid-initial-values-in-field-declarations

but it's true that the initialize won't be called again, i think we have 2 options here:

• create a new initialise fn: e.g initializeV2 which only initializes this variable
• or just make sure that we call the setUserOpMaxCost and the migration.

thoughts?

[fedealconada]

also, this is interesting. when upgrading a contract:

• you cannot change the order in which the contract state variables are declared
• you cannot change the type of a variable
• you cannot change the type of a variable
• you cannot introduce a new variable before existing ones
• you cannot remove an existing variable

If you need to introduce a new variable, make sure you always do so at the end:

we may need to re-visit our last changes on the contracts and maybe revert the changes (if there are) and re-deploy? or maybe not? they've been working fine...

we should ideally also make sure that all tests run locally but also on mainnet fork (on the deployed contracts)

[rrecuero]

Yes, I have been taking care to follow this. It is what we did at Babylon. Always add at the end

you cannot change the order in which the contract state variables are declared
you cannot change the type of a variable
you cannot introduce a new variable before existing ones
you cannot remove an existing variable

[rrecuero]

One comment about initialization. Otherwise, lgtm

[codecov]

Codecov Report

Attention: 1 lines in your changes are missing coverage. Please review.

Comparison is base (7d5918c) 93.82% compared to head (ebd6fb8) 94.34%.
Report is 1 commits behind head on main.

❗ Current head ebd6fb8 differs from pull request most recent head d5134ef. Consider uploading reports for the commit d5134ef to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #58      +/-   ##
==========================================
+ Coverage   93.82%   94.34%   +0.52%     
==========================================
  Files           8        8              
  Lines         437      442       +5     
  Branches      121      122       +1     
==========================================
+ Hits          410      417       +7     
  Misses          2        2              
+ Partials       25       23       -2     

Files	Coverage Δ
src/paymasters/SponsorPaymaster.sol	92.85% <100.00%> (+1.68%)	⬆️
src/wallet/KintoWalletFactory.sol	96.36% <100.00%> (+1.91%)	⬆️
src/wallet/KintoWallet.sol	91.96% <83.33%> (+0.14%)	⬆️