validate yaml for forbidden extra fields

[andreasjansson]

also small optimization to reuse test model instead of repushing if both train and predict are set.

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🚀	This description was created by Ellipsis for commit 726a1b3

Summary:

This PR forbids extra fields in YAML configurations and optimizes model reuse to avoid redundant pushes, with added logging for prediction URLs.

Key points:

• Added ConfigDict(extra="forbid") to TestCase, FuzzConfig, PredictConfig, TrainConfig, and Config classes in cog_safe_push/config.py to forbid extra fields in YAML.
• Optimized model reuse in cog_safe_push/main.py by introducing reuse_test_model to avoid redundant pushes when both train and predict are set.
• Updated cog_safe_push function to handle reuse_test_model parameter.
• Added logging of prediction URL in cog_safe_push/predict.py for better traceability.

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