Add unit tests for GeoUtils — distanceMiles and fuelLabel

[GavT]

Summary

GeoUtils.kt contains pure functions distanceMiles() (Haversine formula) and fuelLabel() (fuel code mapping) with no test coverage.

What to test

File: backend/src/main/kotlin/uk/co/fueller/backend/GeoUtils.kt

Test	Description
distanceMiles_zeroForSamePoint	Same lat/lon → 0.0 miles
distanceMiles_londonToManchester	Known distance within ~1% tolerance
distanceMiles_antipodal	~12,450 miles for opposite points
fuelLabel_E10	Returns "Unleaded" or expected label
fuelLabel_B7	Returns "Diesel"
fuelLabel_unknown	Returns raw code or graceful fallback

Workstream: WS2 Phase 2A