Tapdancing (use pedalboard as backend)

[bmcfee]

#1 lists several deformations left to implement here, and we currently rely on some ad-hoc constellation of backends to implement what we have now.

It looks like pedalboard is on track to cover a large swath of the functionality we need from the audio side. Switching our backend processing over will simplify things, make it easier to cover more transformations, and make the whole project a bit more maintainable.

In the short term, it ought to be an easy switch. The only thing to be careful of is the parallel implementation of annotation transformations to match the audio.

In the longer term, it might be worth doing some kind of deferred processing of audio instead of making intermediate copies of the signal. The present implementation doesn't support this, but it could be more efficient if we provide some kind of lazy evaluation / pedalboard constructor that only generates audio when necessary.