Expand HLS segment name metadata

[toots]

This PR expands the metadata available when returning HLS segment's name. Most specifically, it ads the segment's duration, in seconds (float) and in ticks (main ticks).

With these changes, it is now possible to keep track of a segment's duration in its filename:

def segment_name(metadata) =
  "#{metadata.stream_name}_#{metadata.duration}.#{metadata.extname}"
end

This data is only available when closing the segment so the filename computation is delayed until the segment is being closed.

To prevent the segment_function from further breakage if/when adding more data, its signature is changed to a single record containing all the available attributes.