feat: refine PythonInterperter to proper take out the exception arguments

[lxdlam]

• The code introduces a bridge function to forward exception arguments directly to the dspy side manager.
• Implement a smolagents-inspired FinalAnswer exception, allowing user code to call final_answer() for a clean, non-local exit. The manager captures this to produce a structured final output rather than relying on stdout, particularly beneficial for complex generated code. Add corresponding unit tests to cover new functionality.
• Minor enhancements included (see code for details).