Analyse test stream, enumerate all features, and work out what we need for corosio testing.

[MungoG]

note: we may want to include real socket testing facilities.

[sgerbino]

The test infrastructure has been built out:

• make_socket_pair() for real TCP socket testing via loopback
• mocket class for mock socket testing with staged data and expectation validation
• make_mocket_pair() for hybrid real/mock testing with error injection via fuse
• stream_tests.hpp with generic test_echo() and scaled_test_data() helpers
• All facilities are coroutine-native and parallel-test safe (ephemeral ports)

These are actively used across socket, TLS, and stress tests.