Patch UpgradeableRenounceableProxy to strictly enforce promises

[roleengineer]

Refactor _delegate function to prevent modification of admin and implementation slots.

This patch ensures that the proxy-native functions upgradeToAndCall and renounceUpgradeability are exclusive by disallowing any adjustments to the admin and implementation slots during implementation execution. This change enforces strict integrity of these slots, preventing modifications during delegate calls.

[roleengineer]

Actually, i start thinking now that ADMIN_INIT immutable lost its meaning and probably should be removed. Let me think a little, probably i'll do one more commit.

[roleengineer]

Finally decided to remove ADMIN_INIT, ready for merge.

[benjaminbollen]

some points to explicitly state to have confirmed, as we are now knee-deep into this:

1. L96-98, just to explicitly confirm: we do want the admin to be able to access the implementation. We could for security be strict and only allow the admin to access the proxy admin functions in _dispatchAdmin() - and revert for unknown signatures. But for our intended use the groupAvatar should also be the one that (if any governance) has the governance on the policy implementation. So I think this is our correct and intended behaviour.

2. Related to the first point, should we consider re-entrency scenarios in this proxy contract; specifically to the admin functionality? I think all is good; would it be valuable to have for all policies (using this proxy) regardless?

3. we emit the ERC1967 events in the open zeppelin calls. so that's good!

4. we could implement a time-delay for upgradeToAndCall functionality, but I think that's over-engineering at this point for our needs. Recommending and guiding people to meaningfully use a SAFE multisig as groupAvatar is imo sufficient for us

5. ERC1967 lib already checks that upgrading to a new implementation checks that is has codeLength > 0; as a soft sanity check. So that's covered.

This looks very good; if we agree/discuss on point 1. and 2. (which i think we do); this is good to merge!

great work!

[benjaminbollen]

LGTM!

[roleengineer]

After spending additional time to knee-deep, we concluded that the proxy admin functionality should be protected by a reentrancy guard to prevent potential vulnerabilities.