Add CSV export for route summary

[RitikaSen27]

Summary

Adds CSV export functionality for route summaries and unit tests for the distance() and time_diffs() utilities.

Changes

• Implemented write_summary_to_csv() in RouteParams
• Added --export-csv CLI argument
• Updated execute_routing() to support optional CSV export
• Added analytical unit tests for distance() and time_diffs() using a simple meridian route

Motivation

CSV export allows users to easily load optimized route summaries in tools like Excel or pandas without parsing GeoJSON.
The added tests ensure the distance and time calculations remain stable and prevent regressions.

PR Checklist:

In the context of this PR, I:

• have (already previously) filled the 52North Contributor License Agreement and received positive feedback on this matter
• have filled the 52North Contributor License Agreement and am waiting for feedback
• provide unit tests embedded in the WRT test framework (WeatherRoutingTool/tests) that allow the simple testing of the new/modified functionalities. All (previous and new) unit tests execute without new error messages.
• ensure that the code formatter runs without errors/warnings
• ensure that my changes follow the WRT’s guidelines for contributing at the time of the contribution

Please consider that PRs which do not meet the requirements specified in the checklist will not be evaluated. Also, PRs with no activities will be closed after a reasonable amount of time.