Use nanosecond instead of Millisecond precision
Use nanosecond instead of Millisecond precision

media.SampleBuilder would round time and was breaking audio samples that
required higher precision. This was seen only with alaw/ulaw that needed
microsecond precision. v3 had only been used with Opus so far.

Resolves #1640

pion/webrtc,pion/webrtc,pion/webrtc,pion/webrtc