Add configurable and inferred base coords for address resolution

[eifinger]

Summary

• add optional base_coords parameter to calc_routes() to control Waze address resolution anchoring
• pass optional base coordinates through to address_to_coords()
• when base_coords is not provided and exactly one endpoint is already coordinates, use that endpoint as the base for resolving the address
• add tests for explicit custom base coordinates and automatic coordinate-endpoint fallback
• document the new behavior in README.md

Validation

• uv run pytest -q

Attribution

Inspired by @SylvainM98

[SylvainM98]

Thanks for the credit, glad it helped ! 👍