EVM: add FA withdrawal struct and helper methods

What

This MR adds FA withdrawal structure which contains information for creating an outbox message.

Why

FA withdrawal encapsulates multiple fields within a single structure, providing several useful helpers for parsing and encoding.

How

This is a non-breaking change, kernel execution flow is not affected by this MR.

Manually testing the MR

make test

Checklist

• Document the interface of any function added or modified (see the coding guidelines)
• Document any change to the user interface, including configuration parameters (see node configuration)
• Provide automatic testing (see the testing guide).
• For new features and bug fixes, add an item in the appropriate changelog (docs/protocols/alpha.rst for the protocol and the environment, CHANGES.rst at the root of the repository for everything else).
• Select suitable reviewers using the Reviewers field below.
• Select as Assignee the next person who should take action on that MR