feat: add a native Syslog transport

Zario's roadmap includes native Syslog support. This is a good contributor-sized feature because it can be implemented as an isolated transport without changing the core logging API.

Goal

Add a SyslogTransport that can send Zario log records to a local or remote syslog endpoint.

Suggested scope

• Support UDP first; TCP can be a follow-up if it makes the initial implementation too large.
• Map Zario levels to sensible syslog severities.
• Allow configuration for host, port, facility, and app/service name.
• Reuse the existing transport interface/lifecycle conventions.
• Make failures predictable and compatible with flush() / close() where applicable.

Acceptance criteria

• SyslogTransport is exported from the appropriate transport entrypoint.
• Unit tests cover level mapping and payload formatting.
• A test verifies delivery to a local test socket without requiring an external syslog server.
• Documentation includes a minimal usage example.
• Existing Bun and Node compatibility tests continue to pass.

Non-goals

• Full RFC edge-case coverage in the first PR.
• TLS/TCP support unless the contributor wants to include it cleanly.
• Changing the public logger API.

If you want to work on this, comment on the issue with the scope you plan to tackle so we can avoid duplicate work.

Start by locating the existing transport interface, lifecycle conventions, and transport entrypoint, then review the current unit and Bun/Node compatibility tests. Implement the isolated UDP Syslog transport with configurable host, port, facility, and app name, and verify level mapping, payload formatting, local-socket delivery, exports, documentation, and flush/close behavior.