Refactor audio with a dedicated Sampler

[JD557]

Moves the AudioClip/AudioWave iterator methods to a new Sampler class.

The reasons for this are the following:

• There was a huge performance problem introduced in Improve audio player performance #356, where AudioWave#drop was pretty much broken for waves generated for oscillators. Turns out that I would need to add more iterator special cases.
• The original reason to have the iterator methods was to allow streaming data from audio files, but that doesn't make much sense with the current interface, which pretty much promises random access to the clip.

As such, I decided to simplify the code and make those methods agnostic of the underlying AudioWave/AudioClip implementation.

Also, for now I'm considering streaming audio out of the scope for Minart. It's still possible for an application to implement that using something like a Iterator[AudioClip] or a Stream[AudioClip]`, but I imagine each application will have their preferred format.

I also did some tests with HyperLoopRunner on Firefox and now the audio seems good, so I think this should close #354

Finally, this also fixes a bug with AudioPlayer#play(wave, channel), which was always using channel 0.