[Feature] Cleaner API specifically for getting generated prompt

### What feature would you like to see? Currently, it seems there is no specific API to obtain the prompt generated by DSPy cleanly other than inspect_history(). Would be nice if there is an API added specifically for this purpose because it can make integration more flexible with different frameworks or toolkits (e.g. Google ADK), etc. ### Would you like to contribute? - [ ] Yes, I'd like to help implement this. - [x] No, I just want to request it. ### Additional Context _No response_