This will make it possible to run background tasks in a type safe way.
Sadly, this does mean that every plugin now needs to define the type
alias and constructor function since Rust does not yet support defaults
for associated types.
Instead of the previous technically-unsound approach. While it wouldn't
cause any issues in practice, it did break Rust's guarantees. That was a
design choice after adding support for editors in NIH-plug, but this is
probably the better long term solution.
The downside is that all uses of `param.value` now need to be changed to
`param.value()`.
The FIR crossover will need to use FFT convolution, so it can't use the
same loop. Because of that we'll need to rework the FIR crossover to not
use channel SIMD and to work on channel slices instead.
The low frequency performance is too poor at this filter size and the
DSP load impact is too high. This needs to be implemented using FFT
convolution instead.