Add detailed error message for missing model configurations

[shenchucheng]

Features

• Added command-line flags --opt_model_name and --exec_model_name to specify models for optimization and execution tasks.
• Improved the exception handling with more detailed error messages when the models are not found in the configuration file.

Result

python -m examples.aflow.optimize --dataset MATH --opt_model_name claude-3-5-sonnet-20240620 --exec_model_name gpt-4o-mini

[didiforgithub]

LGTM

[stellaHSR]

LGTM