Port to thread safe version of rust-vst

In https://github.com/askeksa/rust-vst/commits/thread_safe_plugin I have made a proposal for making the rust-vst crate safe.

It could be very interesting to see how this crate could be ported to the new API, in particular in regards to how it could ease some of the parameter communication which is made more complicated by the change.

Pull request is here: https://github.com/rust-dsp/rust-vst/pull/65

Start by reviewing the thread_safe_plugin commit history in askeksa/rust-vst and the referenced rust-dsp/rust-vst pull request #65. Compare the proposed new API with easyvst's current implementation and identify how parameter communication is affected. Done means the crate is ported to the thread-safe API with parameter handling preserved, but the issue does not name specific files or tests.

Written by the indexing model from the issue text.