Added AudioTap functionality

[bsneed]

• Added AudioTap class.
• Added AudioPlayer.audioTap variable.
• Taps are only actually changed when a AVPlayerItem is being observed.
• Clients can subclass AudioTap to retrieve the audio frame/buffer data.
• Added simple lifecycle test
• Depends on Added macOS support & example #79
• Fixes Expose current buffer for visualisation/waveform rendering #50

[dcvz]

@bsneed your PR #73 there's also been some changes to add CI workflow for macOS. Would you mind rebasing? since your PR was squashed commit the easiest way will be to just apply the commits that changed:

git rebase --onto main HEAD~X where X is the number of commits different than the base branch that got merged.

[bsneed]

Heya @dcvz, thanks! Just updated and will keep an eye on the CI here.

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[dcvz]

@bsneed I'll try to review this today or over the weekend. I've updated the example app you started to be universal for both platforms. It would be really cool to have a usage of the taps on it (a simple waveform?) in case you're interested. It's not mandatory for merge though.