Update event processing code in BlepSynth for sample accurate event processing

[swesterfeld]

Since we now have sample accurate parameter updates (in addition to sample accurate midi events), I updated the blepsyntht code to handle this by processing events between audio rendering where appropriate. This branch also checks the ordering of the event stream and prints errors to stderr if the order of the events is invalid. This currently happens for my version of Anklang, and needs to be fixed elsewhere.

[tim-janik]

This branch also checks the ordering of the event stream and prints errors to stderr if the order of the events is invalid. This currently happens for my version of Anklang, and needs to be fixed elsewhere.

That is fixed in the QueueMultiplexer iterator in recent trunk.

[tim-janik]

Please make sure the CI succeeds, that makes merging simpler. If you suspect a spurious CI failure, you can simply re-trigger the CI run (or request that I do it for contributors that lack collaborator perms).