feat: add Unix socket connection support using unix:// URL format

[lightrabbit]

Summary

• Add Unix socket connection support using the unix:// URL format
• Unify URL parsing logic by converting to URL objects first, then processing, to avoid code redundancy
• Update README documentation to explain Unix socket usage

Usage

// Connect via Unix socket
const client = new SupervisordClient("unix:///tmp/supervisor.sock");

// With authentication
const client = new SupervisordClient("unix:///tmp/supervisor.sock", {
  username: "user",
  password: "password",
});

Notes

• Unix socket support is available on Linux and macOS only
• URL format is consistent with supervisorctl's serverurl configuration