feat: initial SOCKS5 proxy with chain support

Asyncio-based SOCKS5 server that tunnels connections through
configurable chains of SOCKS5, SOCKS4/4a, and HTTP CONNECT proxies.
Tor integration via standard SOCKS5 hop.

TODO.md

@@ -0,0 +1,26 @@
+# s5p -- Backlog
+
+## Features
+
+- SOCKS5 BIND and UDP ASSOCIATE commands
+- Chain randomization modes (random, round-robin)
+- Per-destination chain rules (bypass chain for local addresses)
+- Hot config reload on SIGHUP
+- Systemd socket activation
+
+## Performance
+
+- Benchmark relay throughput vs direct connection
+- Tune buffer sizes for different workloads
+- Connection pooling for frequently-used chains
+
+## Security
+
+- Optional SOCKS5 server authentication
+- Rate limiting per source IP
+- Access control lists
+
+## Docs
+
+- Man page
+- Architecture diagram