Proto/Michelson: implement CONTRACT for SCORU addresses

Context

Here we implement #2800 (closed), i.e. CONTRACT for SCORU addresses. It looks much more like CONTRACT for originated contracts than for TORU because we rely on entrypoints defined in the type registered at origination.

Based on !5474 (merged)

Manually testing the MR

See added tests

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