Function valid_opus_duration 

pub(crate) fn valid_opus_duration(ms: f64) -> bool

True if ms is a valid Opus frame duration (2.5, 5, 10, 20, 40, or 60 ms).

The comparison is done in tenths of a millisecond (round(ms * 10)) so the fractional 2.5 ms case is accepted exactly, without float-equality pitfalls.