Message for Notifying about Hooks/Non-Tests

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## Summary

A new message that can publish information about hooks/Non-Tests

## Background and Motivation

Currently if a hook fails, I have two options:
- attach the failure to an existing test node
- create a dummy test node to represent the hook

Those problems with these are, respectively:
- this implies the test failed which isn't the case, and it also complicates code bases more as the test object must be kept around for longer, and also timings. Do I count hook timings in the test that triggered it? Ideally no, it would have its own object with it's own timing.
- dummy test nodes are reported as new tests, and would then show under the test counters at the end, and IDEs would show them as runnable tests.

## Proposed Feature

A new message to represent hooks would be nice.

It would simplify my logic as I wouldn't have to keep test objects around for longer and delay their result publishing until hooks had finished.

Optionally, supplying a property of test IDs to them could represent what tests they relate to/trigger from. These could be used to drive IDE uis if they wanted to build something to show hook execution.

No files, tests, or entry points are named. Start by reviewing the existing message model and hook-result publishing path, then define the protocol and acceptance criteria for a hook message, including whether related test IDs are required; done means hooks are represented without appearing as failed or runnable tests.

Written by the indexing model from the issue text.