Fix new compile + test warnings for Openzeppelin plugin & Solhint

[kyzooghost]

Description

After #656 was merged where we updated the versions of multiple contract dependencies including Solhint and @openzeppelin/upgrades-core, we have had a bunch of new warnings emerge in contract compilation, tests and linting. We would like to address these new warnings.

Motivation

Better developer UX with less warnings, also more aligned with current 'best practices'

Tasks

• Address Solhint and warnings

Acceptance criteria

• Passing CI

Risks

• Break CI

Remember to

• Add the documentation label in case there is an impact on the documentation
• Add priority and team labels
• Add Task for updating the Runbook or adding/updating existing metrics and alerts.