Formal verification: Fix unresolved setup call from the harness constructor

[mmv08]

While debugging our failed runs in https://github.com/safe-global/safe-contracts/pull/641, @jhoenicke pointed out in our shared Slack channel, that there was an unresolved call in the constructor method. There was a solidity compiler warning, but I previously checked this with the Certora team, and they deemed this one OK in the prover context.

This PR fixes it by munging the visibility from external to public for the setup method and also adjusting the storage location of the variables passed to the method to be callable from the constructor.

Many thanks to @jhoenicke 🙂

[github-actions[bot]]

Pull Request Test Coverage Report for Build 5974123615

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 93.191%

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Totals
Change from base Build 5892512694:	0.0%
Covered Lines:	320
Relevant Lines:	340

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