Add dynamic port allocation for Flask server to avoid port conflicts

[Yin-SHT]

Summary
Adds automatic port detection and switching functionality to prevent port conflicts when running the trace collection script.

Problem
The script hardcodes port 1234 for the Flask server. If the script terminates abnormally (crash, force kill, etc.), the port may remain occupied, causing subsequent runs to fail.

Solution
Implemented automatic port detection and fallback mechanism:

1. Check if default port (1234) is available before binding
2. Automatically try alternative ports if default is occupied
3. Display which port is being used for better debugging