Update skip silence algorithm

The updated algorithm has two main improvements:
 - The silence padding is not constant but a ratio of the original
   silence (up to a defined max) to more naturally represent the
   original gaps.
 - The silence is not instantly going to zero, but uses a ramp down
   and up for a smooth volume transition and also retains a small
   percentage of the original noise for more natural "silences" that
   still contain some background noise.

#minor-release

Issue: #7423
PiperOrigin-RevId: 602322442