Non-blocking send queue on EAGAIN

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PR: Outbound send queue on EAGAIN

Summary

Replace the single deferred packet buffer with a per-player outgoing queue so sends remain ordered and non-blocking. Packets are sent immediately when possible and queued only when the socket returns EAGAIN/EWOULDBLOCK.

Key changes

• Added out_packet_t and per-player queue pointers in include/UCraft/player.h, removing the legacy packet_dispatch_event path.
• Updated sendData() to report blocking via an out param and return early on EAGAIN/EWOULDBLOCK.
• Implemented queueing and flushing in src/socketio.c, with cleanup of queued packets in src/player.c.
• Simplified the send loop in src/UCraft.c to sendDispatch() + sendFlush().
• Moved errno include to include/UCraft/wrapper_unix.h and include/UCraft/wrapper_win.h after removing it from include/UCraft/socketio.h.

Behavior

• If the socket is writable, sendDispatch() sends immediately and does not queue.
• If a send blocks, the unsent tail is queued and later flushed in order by sendFlush().

Note

AI assistance was used during the implementation (codex). Human intervention was involved though!