Add unit test coverage for external source ingestion and core pipeline logic

[ZeroQuest]

Introduce unit tests validating ingestion logic and source resolution behavior for all supported sources.

Done when:

• Unit tests exist for Open-Meteo source resolution
• Unit tests exist for NOAA source ingestion (via web CSV flow)
• Unit tests exist for HTTP JSON ingestion
• Unit tests validate source resolution logic
• Unit tests validate time filtering behavior
• Tests run successfully using pytest