feat(gateway): support multi-port TCP listening via port ranges

[kvinwang]

Summary

• Allow listen_port to accept either a single port (8443) or a range string ("8443-8543") to bind multiple TCP listeners
• Round-robin poll across all listeners to avoid starving any port
• Remove single-port port field from HostInfo proto (no longer meaningful with port ranges)
• Use {e:#} for cleaner connection error logs

Context

Under high concurrency (>60K connections per port), a single listen port can exhaust its accept queue or cause kernel-level backlog issues. Binding multiple ports distributes incoming connections across more kernel data structures.

Load testing confirmed: 20 ports handled 200K concurrent TLS connections at 100% success rate.

Config example

# Single port (backwards compatible)
listen_port = 8443

# Port range
listen_port = "8443-8462"

Test results

• Deployed to gateway CVM with listen_port = "14100-14110"
• Gateway bound all 11 ports (14100-14110), confirmed via /proc/net/tcp
• TCP connections to non-default ports (e.g., 14105) succeed from host
• Backwards-compatible single port config continues to work