Yes - add silence detect

Replaces https://github.com/amiaopensource/audioqc/issues/28: Note to add silence detect to check for things like excessive silence at heads/tails as well as empty stereo channels. @susiecummings thoughts on any other uses?

No files, tests, or entry points are named. Start by reviewing the repository's existing batch audio QC checks and clarify the intended silence criteria with the maintainers, including excessive silence at heads and tails and empty stereo channels. Done means the agreed checks detect those cases and are covered by tests.

Written by the indexing model from the issue text.