zitilib: ZIti_connect honor socket non/blocking status

[ekoby]

[fixes #984]

1. Non-Blocking Ziti_connect and Ziti_connect_addr.
   The core zitilib connection functions have been redesigned to support non-blocking operations:

   • Asynchronous Initialization: Instead of blocking until a Ziti connection is fully established, these functions now initiate the process in a background worker thread.
   • Ephemeral Bridge: They create a local ephemeral "bridge" socket and immediately return the result of a standard connect() to this bridge.
   • Standard Multiplexing: If the application socket is non-blocking, Ziti_connect will return EINPROGRESS (or WSAEWOULDBLOCK on Windows), allowing applications to use select, poll, or epoll to monitor connection
     progress.

2. IPv6 Support

   • The internal bridge mechanism now supports both IPv4 and IPv6 loopback addresses.
   • New utility function zl_socket_af identifies the address family of a given socket to ensure the correct bridge type is created.

3. Cross-Platform Consistency & Stability

   • Background Bridging: Connection bridging now utilizes uv_queue_work to prevent the Ziti event loop from being blocked by synchronous socket operations.
   • API Refinement: ziti_conn_bridge_fds now uses uv_os_sock_t for better type safety across platforms.

4. Sample Program Updates

• ziti-fd-client: Extensively updated to demonstrate the new non-blocking API, including manual poll() usage and an optional blocking mode via the ZITI_SAMPLE_BLOCKING environment variable.
• ziti-ncat: Updated to align with API changes and ensure stable connection handling.

[dovholuknf]

should this be done in ziti_lib_init on windows? or should ziti_lib track that it's been called somehow? it seems important to do (since you're doing it here). how would python or any other FFI handle this? does it need to?

[ekoby]

this is a sample app and it is opening socket before Ziti_lib_init()

[dovholuknf]

one leak question wrt req->conn but other than that lgtm