Handle packet stream EOF without StopIteration

[keilogic]

Summary

• catch StopIteration from pcap.next() and end PacketStreamer.read_interface() normally
• keep the existing not header EOF path and packet stats reporting intact

Tests

• python -m py_compile chains\sources\packet_streamer.py
• python -m flake8 chains\sources\packet_streamer.py --max-line-length=140
• fake-pcapy runtime probe: pcap.next() raises StopIteration, list(streamer.output_stream) returns [] without a generator RuntimeError
• git diff --check

Fixes #9