Dedicated types for internal operation results

Context

This is the second step to answer #2806 (closed).

Some dedicated types are created for internal operation results.

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): no semantics changes, so existing tests still cover the modifications.
• 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): no new features.
• Select suitable reviewers using the Reviewers field below.
• Select as Assignee the next person who should take action on that MR