RecordPlugin.renderMicStream overinitializes AudioContext

[jaredjj3]

This is just a nit, I'm not sure if it actually matters. Feel free to close.

From MDN docs:

It's recommended to create one AudioContext and reuse it instead of initializing a new one each time, and it's OK to use a single AudioContext for several different audio sources and pipeline concurrently

However, RecordPlugin.renderMicStream re-initializes it every time it's called.

wavesurfer.js/src/plugins/record.ts

Line 100 in f56ea15

const audioContext = new AudioContext()

[katspaugh]

Thanks! PRs are welcome.