feat: eip-4906 interface

[smol-ninja]

Linked issue

• Closes https://github.com/sablier-labs/v2-core/issues/947

I didn't include supportsInterface in interface because its verbose. The Natspec is quite clear.

/// @inheritdoc ERC721
function supportsInterface(bytes4 interfaceId) public view override(ERC721, IERC165) returns (bool) {
    return interfaceId == 0x49064906 || super.supportsInterface(interfaceId);
}

[PaulRBerg]

We can actually put it in the interface by inheriting IERC4906 in ISablierV2Lockup.

This is how it should have always been done.

[smol-ninja]

Any reason why IERC4906 and not just IERC165? Its ERC-165 that defines the standard interface.

[PaulRBerg]

Because IERC4906 interface also contains the MetadataUpdate and the BatchMetadataUpdate events, which we need.