Complete unit test coverage for upgradeable renouncable proxy

[roleengineer]

Two mock contracts were implemented to test the behavior of the upgradeable renounceable proxy under different scenarios:

• Mock with Selector Clashes: This mock simulates cases where there are selector clashes between the proxy and implementation, allowing us to test how the proxy handles such situations.
• Mock with Stateful Implementation: This mock simulates an implementation which works with state, allowing us to evaluate how the proxy handles state.

Tested:

• Proxy's Native Functions: all native proxy functions to ensure their correctness in various scenarios, including when selector clashes or a stateful implementation are present.
• Behavior with Clashing Implementations: how the proxy behaves when the implementation contract has selector clashes, leading to potential vulnerabilities or unexpected behavior.
• Behavior with Stateful Implementations: how the proxy behaves with a stateful implementation, ensuring it handles state correctly.

During testing, a serious issue was discovered where the proxy's native functionality can be bypassed by a malicious implementation. Specifically:

Proxy Admin & Implementation: any address (not just the proxy admin) can change the proxy's admin and implementation. This is a critical vulnerability, if we have a constraint that only proxy native functionality can change admin and implementation.

Given the findings, conclusion is that fixes are required in the proxy contract to address these security issues and ensure the integrity of the upgradeable renouncable proxy functionality.

[roleengineer]

solves #90

[benjaminbollen]

Great work!

I left small questions, you can see whether they need resolving or not; happy to merge following your response

[benjaminbollen]

I can't believe I never realised using an absolute path is so much more readable and better. Internal style-guide updated !

[benjaminbollen]

both questions resolved. LGTM!