Test support utilities

Enabling the test-support feature unlocks helpers intended for integration and unit tests:

• MemoryStore: in-memory PoiStore performing linear scans for small datasets.[^11]
• UnitTravelTimeProvider: deterministic provider returning one-second edges, useful for reproducible solver fixtures.[^12]
• TagScorer: reference Scorer that sums theme weights based on tag keys, demonstrating how to convert tags into scores.[^13]