feat: plugin and chain log

[PaulRBerg]

Implements #19, #36, and #37.

@andreivladbrg, you can disregard the fact that the ChainLog contract is incomplete and untested. The goal was to implement an MVP to show case my rationale.

I managed to fully test the ChainLog contract.

[andreivladbrg]

Let's not ignore the lockup parameter in the onStreamCanceled function:

Code Snippet

    function onStreamCanceled(
        ISablierV2Lockup lockup,
        uint256 streamId,
        address, /* recipient */
        uint128 senderAmount,
        uint128 /* recipientAmount */
    )
        external
        noStandardCall
    {
        // Checks: the caller is Sablier.
        if (!chainLog.isListed(address(lockup))) {
            revert Errors.SablierV2ProxyPlugin_CallerNotSablier(address(lockup));
        }

        // This invariant should always hold but it's better to be safe than sorry.
        address streamSender = lockup.getSender(streamId);
        assert(streamSender == address(this));

        // Effects: forward the refunded assets to the proxy owner.
        IERC20 asset = lockup.getAsset(streamId);
        asset.safeTransfer({ to: owner, value: senderAmount });
    }

Very nice idea with the new abstract contract, but I think it would be better if we renamed NoStandardCall to something like OnlyDelegateCall. The term "Standard" doesn't provide enough clarity since many things can be considered standard, let's be more precise.

No tests for SablierV2ChainLog.

[PaulRBerg]

Let's not ignore the lockup parameter in the onStreamCanceled function:

Actually, we will ignore it. See sablier-labs/v2-core#470.

Very nice idea with the new abstract contract, but I think it would be better if we renamed NoStandardCall to something like OnlyDelegateCall

Thanks. I agree with your suggestion.

No tests for SablierV2ChainLog.

See my top comment.

[PaulRBerg]

I have made a few improvements, and also written tests for SablierV2ChainLog.

@andreivladbrg, can you please review when you have a moment.

[andreivladbrg]

I think there is a mistake, either here:
https://github.com/sablierhq/v2-periphery/blob/82385cd7916335468e7dfa1f36730076d05bba2b/src/SablierV2ProxyPlugin.sol#L37
or here:
https://github.com/sablierhq/v2-periphery/blob/82385cd7916335468e7dfa1f36730076d05bba2b/src/SablierV2ChainLog.sol#L29

[PaulRBerg]

I think there is a mistake, either here:

Yep, you're right. ISablierV2ProxyPlugin has three inherited components. I will fix this.

[PaulRBerg]

@andreivladbrg - I have addressed all of your feedback above. Is this PR good to merge now?

[PaulRBerg]

Good to merge now, @andreivladbrg?