feat: Add speed control

[DoozkuV]

This PR allows you to increase or decrease the speed of the audio playback by setting the "playback_speed" variable like what was referenced in #41.

[cheofusi]

Hi George,

Thank you for the PR!

How did you test this?

[DoozkuV]

Hello! Thank you for the response. To be honest, I made this PR as I was working on a really simple metronome CLI application and I was frustrated by the lack of extremely simple audio libraries for Python. This one caught my eye, but I saw it didn't have a good speed control option which is why I decide to jump in and implement it myself. It's my first time doing this kind of C/Python FFI work though so apologies if the PR is a bit rough.

Right now there's a SIGSEGV issue when you change the speed around with high numbers, so I'm going to go back in and work on that some more. I'll also try to get some better testing set up because I didn't catch that when I first sent this PR. Thank you for your patience!