[Platform] Implement event queu cleanup on unit test teardown.

[lpbeliveau-silabs]

Reproduction steps

When adding a new test to the CI unit test, if unprocessed events remain in the platform manager's event queue, they will persist into the following tests. This is will impact the time DrainAndServiceIO() takes to process events in the queue and leads to failure when executing CI unit test for OpenIoT SDK as the tests are ran in a single file.

To reproduce the steps, the TestReportScheduler on the CI and it will cause TestAclAttribute to fail on:
src/app/tests/TestAclAttribute.cpp:251: assertion failed: "delegate.mGotReport"

Which is expecting the report to be processed after DrainAndServiceIO() was called.

It is unclear what exactly is causing this behaviour but it is reproducible by having unprocessed events on in the queue at the end of previously executed tests.

Platform

other

Platform Version(s)

No response

Type

Unit tested, CI tested

(Optional) If manually tested please explain why this is only manually tested

No response

Anything else?

No response

[Alami-Amine]

a fix (workaround?) was found to this issue, just putting it here for reference. If we think this is ok we can close the issue.