test: add timer loop tests

test: add timer loop tests

We've been experiencing timer hangs with mingw-llvm.
std::condition_variable::wait_for was returning a few microseconds
before the requested time and then hanging when called with a
small interval (e.g. microseconds).

This was affecting the OSD periodic tick, which would hang after
a while (20m up to 2h).

The issue can be reproduced with a timer loop and a small interval
(e.g. 40us), in which case the timer is likely to hang after about
10s.

We're adding some tests, while the actual mingw-llvm issue will
be mitigated in a separate commit.

Signed-off-by: Lucian Petrut <lpetrut@cloudbasesolutions.com>