Support feedback once all mock data has been read in Pipe()

[fako1024]

When using the Pipe() construct for mock sources it would be very helpful to know when all data from the "base" source (e.g. a pcap file) has been read / consumed into the "piping" source (e.g. to allow test code to know how much data to expect in the end, which quite often is not known without actually processing it (especially pcap files do not support getting the number of captured packets without full perusal of the data).

DoD

• Add (atomic) construct to allow notification of a consumer (via channel)
• Add tests