It wasn't copying the frame data from the sources to the output frame
correctly, and there was a small period of zeros at the start of the
frame.
I also converted to using a vec of tuples for the two channels to
make it easier to reason about, since some of the issues were related
to the differences sizes calculated from the clock based on the sample
rate
It's a bit weirdly implemented because the Addressable trait doesn't
have access to System, so it has to set a flag on the Bus which is
then checked during the step function in System to activate the
breakpoint if a watched memory location was written to
