LiFi 7683 message handler

[mpetrun5]

Implement LiFi message handler that verifies and signs the Lifi 7683 order fill.

Implementation details

Add lifi-7683 as protocol option in the API and create a handler that will verify and sign the LiFI 7683 order.
To verify the order we should gather the source chain event and create and sign the fill calldata to verify the order.

Testing details

• unit tests
• manual tests

Acceptance Criteria

• we can fill LiFI 7683 orders