feat: callbacks

[0xiamflux]

Callbacks PoC

This draft showcases a complete callback flow where a call originates on the origin chain, triggers execution on a destination chain, and then returns the result to the origin chain, where it is handled with custom logic.

The flow is as follows:

Possible Next Steps

• Having a dedicated library to abstract functionality and facilitate the interaction would be a valuable addition to the ecosystem.

Possible Future Improvements

• Flexible Callback Contexts: Introducing a more complex data structure to support features like expiration times or additional metadata.
• Robust Error Handling: Supporting logic to handle both successful and failed callbacks.

[0xDiscotech]

Only focus on Callbacks and Callbacks.t.sol files. The other diff won't be a diff anymore once the entrypoints branch is merged on the OP repo.
Will merge with develop by then to solve any possible conflict or any other difference

The base branch was changed.

The base branch was changed.

[0xDiscotech]

Closed in favor of a cleaner PR #162