Chore: Update solidity version from ^0.8.9 to ^0.8.16

[roxdanila]

Context

Closes #305

The code is compiled with Solidity 0.8.9 or higher. For deployment, we recommend no floating pragmas, i.e., a specific version, so as to be confident about the baseline guarantees offered by the compiler. Version 0.8.9, in particular, has some known bugs, which we do not believe to affect the correctness of the contracts.

Changes proposed in this pull request

Update solidity version from ^0.8.9 to ^0.8.16

Test plan

Compiled the contracts and ran all existing tests to check nothing broke.

Checklist

• Rebased the base branch
• Attached corresponding Github issue
• Prefixed the name with the type of change (i.e. feat, chore, test)
• Performed a self-review of my own code
• Followed the style guidelines of this project
• Made corresponding changes to the documentation
• Didn't generate new warnings
• Didn't generate failures on existing tests
• Added tests that prove my fix is effective or that my feature works

Review

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• 🍰 = Nice to have but not essential.
• 💡 = Suggestion or a comment based on personal opinion
• 🔨 = I believe this should be changed.
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• 🚀 = Feedback

[shark0der]

🚢