Add function to get sound file duration

our sound notifications widget needs to know the duration of a sound file (to quieue up multiple notifications), currently its duration is manually defined, but with multiple languages and even sound sets per language.... ugh

No file, test, or entry point is identified in the issue. Start by locating the sound notifications widget and the existing manually defined durations, then determine where sound-file metadata is exposed; done means notification queuing can use computed durations across languages and sound sets.

Written by the indexing model from the issue text.