add ability to adjust playback speed?

[tmratwork]

one of our users requested to slow down playback speed. some of the AI voices we use for generated guided meditations feel too fast. i think i can write this code, although i'm not skilled at coding.

1. any hints on what files i should focus on or how to do it?
2. are there guidelines you would like me to follow to make it easier to offer this feature for others (if you choose to bake it into the main project code)?
3. do i start by forking your project, and then uploading the modified code here?

thanks!