fix: add SO_REUSEADDR to find_free_port to handle TIME_WAIT state

[qykong]

PR type

• Bug Fix
• New Feature
• Document Updates
• More Models or Datasets Support

PR information

The find_free_port() function exhibits inconsistent behavior when trying to bind to recently used ports. Specifically:

• After killing a swift deploy --port 8001 process on port 8001, find_free_port(8001) sometimes returns 8002 (I actually believe it would be better to throw an exception if a port was explicitly specified)
• Re-running the same function immediately after may then return 8001

When a process using a TCP port is terminated, the port enters TCP's TIME_WAIT state for 30-120 seconds (OS-dependent). During this period, socket.bind() fails even though the port is effectively available. Adding SO_REUSEADDR socket option to allow binding to ports in TIME_WAIT state. In fact, this is what has been done within uvicorn as well before launching the server: https://github.com/encode/uvicorn/blob/5e33d430f13622c8363fe74d97963ab37f3df3c2/uvicorn/config.py#L513