Implement input validation in DataGenerator

[moshesham]

Problem

DataGenerator accepts user input without validation:

• num_records can be negative or extremely large
• seed can be any value
• YAML config structure not validated

Impact

• Potential DoS through memory exhaustion
• Unexpected behavior with invalid inputs
• Poor error messages
• Security risk

Tasks

• Add _validate_num_records() method
• Add _validate_config() method
• Add _validate_seed() method if needed
• Call validation methods in __init__()
• Add tests for validation methods
• Add tests for edge cases (negative, zero, very large)
• Update docstrings with validation information

Validation Rules

• num_records: Must be 1 <= n <= 10,000,000
• seed: Must be non-negative integer if provided
• Config must have required keys: 'data_generation', 'fields'
• Each field must have: 'name', 'type', 'values'

References

• PROJECT_REVIEW.md Issue Implement SQL query safety validation to prevent injection vulnerabilities #9