fix(agent, forge): Silence Pydantic v2 protected namespace `model_` warning

[kcze]

Background

After updating to Pydantic v2 Pydantic complains about model fields with model_ prefix as it's a Pydantic protected namespace:

UserWarning: Field "model_info" has conflict with protected namespace "model_".

To silence this warning fields need to be renamed or namespace need to be removed from protected_namespaces.

Changes 🏗️

This PR renames model_* fields to llm_* in affected models.

PR Quality Scorecard ✨

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• [ ] Have you changed the behavior of AutoGPT?   -5 pts
  • [ ] Have you also run agbenchmark to verify that these changes do not regress performance?   +10 pts