Error-monad: fewer names, more explicit names

Context

Part of #1579 (closed)

Some old names have been sticking around in code for a long time. This MR does a little bit of dusting off in the error monad.

Manually testing the MR

N/A

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, the Development Version section of CHANGES.md for everything else).
• Select suitable reviewers using the Reviewers field below.
• Select as Assignee the next person who should take action on that MR