v0.3.0 — session-random DUT destination port

Feature

• The DUT destination port is now optional with a session-random default. Leave --dut-port (or the GUI's Destination port field, which shows random) unset and a single random ephemeral port (IANA dynamic range) is chosen and reused for the whole session; set it and every port-specific test targets exactly that port.
  • config.DUTConfig.target_port is now int | None; random_ephemeral_port() added.
  • The session-scoped dut_config fixture resolves an unset --dut-port exactly once.
  • The CLI echoes the chosen port at startup; the GUI logs it on the first run that picks it.
  • src/runner.py passes --dut-port only when set.

Builds on v0.2.0 (--dut-source-port, and the Custom Packet panel layout fix for maximized windows).

Full changelog: v0.2.0...v0.3.0