Add Travel Time Calculation, Visualization, and Data Export Features

This merge request introduces a complete algorithm for analyzing travel times between stops, generating a heatmap, and exporting results to a CSV file. The algorithm calculates the shortest travel times using Dijkstra’s algorithm and then visualizes these results on a heatmap, making it easy to interpret travel times to various stops. Additionally, the data is saved to a travel_times.csv file, allowing for further analysis outside the application.