If the requested port (default 8000) is already in use, auto-
increment and try the next port, up to 20 attempts. Prints a
message like "Port 8000 is in use, using port 8001 instead".
Previously, if port 8000 was busy, uvicorn would fail with
"[Errno 98] address already in use" and the studio would not
start. Now it gracefully finds the next free port.
Uses socket.bind() to check availability before starting uvicorn.
Cross-platform (Linux, macOS, Windows).
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