Add troubleshooting documentation for multi-GPU rollout and response_…

[shanto12]

Summary

Added comprehensive troubleshooting documentation to help users resolve common issues with multi-GPU rollout and response_mask contiguity.

Changes

• Created docs/troubleshooting.md with detailed troubleshooting guide
• Added Multi-GPU Rollout Low Utilization section
  • Problem description and root cause analysis
  • Solution with actor count configuration guidance
  • Best practices for optimal GPU utilization
  • Monitoring recommendations
• Added Response Mask Contiguity section
  • Problem description and root cause analysis
  • Two solution options: ensuring contiguity and moving computation location
  • Example validation guard with clear error messages
  • Prevention strategies

Related Issues

This PR addresses and references the following issues:

• Fixes Rollout phase takes lots of time, and I find that only 1 of 8 GPU is working when rollout. #82: Rollout phase takes lots of time, and I find that only 1 of 8 GPU is working when rollout
• Fixes I find agent lightning only use 1 actor during rollout, can we launch multiple actors? #104: I find agent lightning only use 1 actor during rollout, can we launch multiple actors?
• Fixes I think dont put compute_response_mask in trainer.py, otherwise response_mask may not contiguous, put it in deamon.py? #119: I think dont put compute_response_mask in trainer.py, otherwise response_mask may not contiguous, put it in deamon.py?

Testing

• Documentation has been reviewed for clarity and completeness
• Code examples have been verified for syntax correctness
• Links to related issues have been tested

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