move deformer state into jams sandbox?

[bmcfee]

Pro:

• Makes everything trivially parallelizable
• Simplifies serialization

Con:

• Difficult to maintain

[bmcfee]

Alternately: thread this through a context manager and pass state objects around the deformers.

[bmcfee]

Following up, this can probably be reduced to a simple pattern.

• BaseTransformer.transform() will acquire an initial state object as a local context manager
• state objects will be passed into all deformers, including audio and metadata. This will make the transformer objects essentially stateless, which simplifies both parallelization and serialization.
• BaseTransformer._transform() will then iterate over self.next(state), which encodes all state-updating logic.