Implement proper MAPE and accuracy calculation methods

- Created calculate_mape() function using proper MAPE formula:
  MAPE = (1/n) * Σ(|actual - predicted| / |actual|) * 100

- Created calculate_accuracy() function using total error ratio:
  Accuracy = (1 - Σ|actual - predicted| / Σactual) * 100

- Updated calculate_results() to store raw actual and predicted values
- Use proper calculation methods instead of shortcuts
- Updated template to accurately describe the metrics