Event handler errors are suppressed by default in tests

When I try using an event in my openedx-platform tests, I found that throwing an exception in an event handler has no effect, and the exception is silently ignored.

This is because openedx-events uses send_robust by default even in tests, which suppresses exceptions thrown in the event receivers. This seems to go against the original intention of https://github.com/openedx/openedx-events/pull/29 which said:

This PR changes which send method to use when sending an event, so they don't fail during runtime. Instead, they will be allowed to fail in a testing/dev environment.

I found that I can work around this by adding EventsIsolationMixin to my test class, and adding this setup code:

    @classmethod
    def setUpClass(cls):
        """Test setup"""
        super().setUpClass()
        # By default, errors thrown in signal handlers get suppressed. We want to see them though!
        cls.allow_send_events_failure(*(s.event_type for s in OpenEdxPublicSignal.all_events()))

But I think that this shouldn't be necessary - suppressing exceptions during tests is confusing and unexpected behavior that takes a while to debug. Also, the code shown above "leaks" because it affects any other tests that will run afterward. The events API provides a way to "allow send events failure" but it doesn't provide a way to undo that.

I recommend that you just scrap all of that and add a setting called SUPPRESS_EVENT_EXCEPTIONS or EVENT_SENDING_ROBUST_BY_DEFAULT which is True in envs/production.py and otherwise defaults to False.

Other issues

1. "allow send events failure" is very ambiguous. Does that mean "allow events to fail, by ignoring their exceptions", or does that mean "allow exceptions (failures) to be reported" ? Calling this "suppress exceptions" would be way more clear.

2. I'm not the only one confused. The documentation of OpenEdxPublicSignal.allow_send_event_failure says:

https://github.com/openedx/openedx-events/blob/34d3fce371f14c892d77284f9fcba8a5e67fc544/openedx_events/tooling.py#L267-L273

But this is the opposite of what it actually does!

https://github.com/openedx/openedx-events/blob/34d3fce371f14c892d77284f9fcba8a5e67fc544/openedx_events/tooling.py#L168-L171

Start by reading openedx_events/tooling.py at lines 168-171 and 267-273, then inspect envs/production.py to understand the current event-sending behavior and configuration. Clarify how exceptions should behave in tests versus production, how the setting should be named, and how the misleading allow_send_event_failure documentation should change. Done means the behavior is consistent with the documented configuration and does not leak between tests.