FR: sorta. Consider splitting out speech preprocessing into a separate crate

[skewballfox]

Hi. Would you consider splitting out the functionality for computing the Mel spectrogram(inside audio.rs) into a separate crate?

This would be useful for other speech-centric models. There are a few libraries for this with ndarray, such as mel-spec and mfcc-rust (contributor), but this is the first implementation I've seen for burn.