Fine-tune prompt templates and add A/B prompt tests

[ziadhany]

• Create prompts/ with versioned prompt templates (e.g., prompts/prompt_v1.py, prompts/prompt_v2.py).

• Build an A/B test runner in test/ab_test.py that runs multiple prompt templates against the same dataset and produces comparative metrics.

• Store results and recommend the best model/prompt per metric.