Factor out data source

[fulldecent]

Progress:

• [x] Create DataSource protocol which could be applicable to audio files or any other data source, such as an array or other generator
• [x] Move all existing audio code into an implementation of this DataSource
• [ ] Use [Float] as the type for the DataSource

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This is nearly done. Please help with the last item if you'd like to get a couple commits in.

[fulldecent]

There is a currently a Swift Evolution that is related here

https://github.com/apple/swift-evolution/blob/main/proposals/0307-allow-interchangeable-use-of-double-cgfloat-types.md

and it might impact the choice of Float above

[fulldecent]

We can use Double now because the proposal above was implemented