[Feature] Add reference documentation

[juntaoyou]

What feature would you like to see?

Added reference documentation to the file:
dspy/predict/parallel.py

Would you like to contribute?

• Yes, I'd like to help implement this.
• No, I just want to request it.

Plan

• Add/expand Google-style docstrings for the above classmethods.
• Include concise usage examples where helpful.

Refs: #8926

Additional Context

No response

[TomeHirata]

Hi, @juntaoyou. Please feel to file a PR!

[juntaoyou]

Thanks. I have submitted a PR #9129

[okhat]

Thank you!