feat(examples): Add example for long-term memory with Qwen

[7Eternity]

This PR introduces a new end-to-end example demonstrating how to use LightMem with a locally-hosted Qwen model to achieve long-term memory.

• Added a new example(run_lightmen_qwen_server.py) in directory examples. - Includes a Python script, sample JSON data, and a detailed README. - The script is self-contained and showcases context consolidation, knowledge updates, and handling of unanswerable questions.