Add feature importance example to random_forest_regression.rs

[noahgift]

Add Part 7 demonstrating feature_importances() method for RandomForestRegressor to improve example consistency and showcase interpretability features for regression tasks.

This makes the regression example consistent with the classifier example (random_forest_iris.rs) which already demonstrates feature importance in Example 5.

Changes:

• Add Part 7: Feature Importance section with housing price example
• Display importance for sqft, bedrooms, bathrooms, age features
• Show practical use cases for feature selection and interpretability
• Update summary to mention feature importance capability
• Renumber OOB section to Part 8

Labels: documentation, enhancement

[noahgift]

Completed in commits 7ceffba and 849ff1d. Feature importance example added to random_forest_regression.rs to match the classifier example.