consider splitting out stft and sundry into it's own crate

[skewballfox]

partially because I myself copied it from Rikorose (with his explicit permission of course), and partially because this has utility outside of our niche use case. We could also expand the options for different windowing functions rather than hard coding one (don't have a signal processing background but apparently there is a lot).

it would be small, covering a small set of functions that are hard to write correctly unless you have the right background (I'm not actually sure if the 1d one is correct, need to verify), and this could pull in a few contributors who work more in that area, but aren't interested or don't have a need for speech preprocessing for ML models.

• link to stft2
• link to stft1
• link to commented out struct containing all state used only for these functions