Add test for round-to-next-second branch.

Applied the same fix to the trim logic in method
TimeseriesUtility.pad_and_trim_trace() as previously applied
to the pad logic. Added a unit test that would have failed
using the old logic.

Fixed some linting errors and made the merge_streams() code cleaner as well as added more unit testing

Cleaned up merge_stream(), takes empty channels out at the beginning and adds them in before the merge() function