Kernel/EVM: add support for inbox framing protocol

Context

Add support for the framing protocol. This is the same as what the kernel is currently doing, except that it adds one additional prefix byte. This will allow e.g. global messages to be defined in the framing protocol in future.

Closes #6151 (closed)

Manually testing the MR

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