Add InvocationError for an error without traceback. Log cancel at info.

[julianstirling]

This needs testing before merge

This fixes two related things:

1. Events being cancelled by the user are logged as errors.

While error handling is used for cancelling the event. From the user's perspective no error happened. They asked for it to be cancelled, and it was. This PR changes that log to "Info", so that the event is logged, but the user isn't notified of an error for expected behaviour.

2. Adds a new exception type without a traceback.

Currently any unhandled errors are shown with an ASGI traceback. Very useful for developers, but not friendly for the end user. These make sense for unknown errors.

In the OpenFlexure Microscope we handle this by catching errors, logging the error and then exiting. This does not notify as an error on exit correctly unless they go to the log. However a full ASGI error traceback doesn't communicate the message needed.

This should create an error type that ends the invocation, logs without traceback, but creates the correct error response when the invocation completes.

Hmm, no they are not always ASGI errors. But, it still seems like a good idea for an action to be able to communicate "I handled this error, but I am stopping" and for this to be treated differently to an unhandled exception in an action.

[barecheck]

Barecheck - Code coverage report

Total: 93.31%

Your code coverage diff: 0.01% ▴

Uncovered files and lines

File	Lines
src/labthings_fastapi/actions/__init__.py	145-146, 412-413, 534-535, 540, 548, 573-574
src/labthings_fastapi/dependencies/invocation.py	161-162

[rwb27]

This looks good to me.

We need to standardise whether exceptions get re-exported from .exceptions or whether they are defined there and imported where they're needed. The latter would play better with the API docs, but we should standardise this in its own PR.