In memory decoding

Hi guys!
I have audio files contents stored in-memory and need to decode audio. In current version all backends accept pathlike argument (which is then passed to `open()`).

Are there any plans to extend your interface to also accept streams of data (e.g. `BytesIO`)?

No files or tests are named. Start by locating the common decoder interface and the backend entry points that currently receive path-like arguments and pass them to open(). Define the supported stream behavior, then verify that the backends can decode in-memory data consistently.

Written by the indexing model from the issue text.