fix(worklet-base): Stop the processor after a dispose message

[tzzo]

An AudioWorkletProcessor is kept alive for as long as its process() returns true, and SoundTouchProcessorBase.process() always did. So once an app disconnects a node and drops it, the processor keeps rendering every quantum and keeps its buffers until the AudioContext closes. Apps that create a fresh node per track — the way to start a new track from empty FIFOs — accumulate one live processor per track for the life of the context.

This adds a { type: 'dispose' } port message. The base processor flips a flag on receipt and returns false from the next render quantum, so the browser can release it. SoundTouchNode, PhaseVocoderNode and FormantCorrectionNode gain dispose(), which posts the message and disconnects the node. None of the subclass processors override process(), so the base change covers all three worklets. DisposeMessage joins the ProcessorMessage union and is exported from @soundtouchjs/worklet-base.

Specs: the base spec covers the flag, the false return and that the pipe is not touched after disposal; the audio-worklet processor spec drives the real processor through a dispose message; each node spec checks that dispose() posts the message and disconnects.

Docs: the four READMEs list the new message and method.

Noticed but left alone, to keep this to one change: the worklet-base README's runtime-message examples use camelCase names (setInterpolationStrategy, value) while the processor matches kebab-case (set-interpolation-strategy, strategy / params).

Model used: Anthropic Fable 5.1

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