Investigating some of the biggest slow downs during tests, the biggest
offender is 'wait_for_stopped' requiring a negative assertion around the
'stopped' event.
It currently waits for a negative predicate to fail before continuing.
This means it must wait for the full DEFAULT_TIMEOUT (50s) before the
test is allowed to continue.
To mitigate this, I added a new `collect_events` helper that will wait
for the given event to occur with the DEFAULT_TIMEOUT, then wait for a
quiet period (0.25s) before returning.
This greatly reduces the amount of idle waiting during tests.
Additionally, looking a the performance of individual test files,
`TestDAP_launch` is the slowest overall test. No individual test is that
slow, but the fact it has so many tests in the same file results in the
test harness waiting for that one file to finish.
To mitigate that, I split `TestDAP_launch` into individual test files
that run in parallel, reducing the runtime locally from over 2mins to
~5s.
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