transcode: SetPCR bugfixes and unit-tests improvements

This merge request fixes a lot of issues found after the merge of the SetPCR integration to the transcode module.
It started from an assert failure being reported to a good amount of bugs being discovered via the unit-tests expansion!

This patchset address the following issues:

• Increase the current max delay value which was too low according to some empirical tests
• Support decoder outputting different frame count than what is provided to them
• Fix PCR fast-forwarding implementation
• Fix the pcr_sync utility support of tracks being extremely in advance compared to the others (see commit logs for details)