Create HSL API integration service

[3nd3r1]

Implement service layer for fetching routes from HSL Routing API (Digitransit).

Technical Details:

• Create app/services/hsl_service.py
  • will use graphql to get stuff from HSL
  • hook into this https://api.digitransit.fi/graphiql/hsl/v2/gtfs/v1
  • atleast get_routes(a, b)
• Implement route fetching with origin/destination coordinates
• Handle HSL API authentication and rate limiting
• Parse and normalize HSL route response format
• Add error handling for API failures

Acceptance Criteria:

• Can query HSL API with coordinates
• Returns structured route data (legs, duration, distance, transport modes)
• Handles API errors gracefully
• Unit tests for HSL service