ProxyProtoSuite starts gost with metadata.proxyProtocol set and asserts
the HAProxy PROXY header is prepended on outbound connections (v1/v2),
backed by a raw-TCP capture script and configs. Add echo754_repro.py
from the hot-reload EADDRINUSE investigation (gost#754).
Bump github.com/go-gost/core to v0.6.1 and x to v0.16.0.
