(fwCore): fix HisResClockTest::getTimeTest

What does this MR do?

Try to use the std::chrono::high_resolution_clock::now() instead of std::chrono::system_clock::now(). As the name space is named HiResClock, it sounds logical...

Although it may be different, especially on macos, it seems that on most platform it is indeed the same, but, as the test failing is not very deterministic, we need some time to validate it. Enjoy

How to test it?

Launch fwCoreTest many many times on all platforms

Associated Issues/Merge Requests

• Issues
  • Closes #141 (closed)