Amend forecast query to be always inclusive for valid_time

[amehta-scottlogic]

This changes the query to get forecast data to be inclusive.

It also makes our unit tests consistent and reduces a lot of repeated code where posssible

[github-actions[bot]]

☂️ Python Coverage

current status: ✅

Overall Coverage

Lines	Covered	Coverage	Threshold	Status
506	447	88%	80%	🟢

New Files

No new covered files...

Modified Files

File	Coverage	Status
air-quality-backend/src/air_quality/api/forecast_controller.py	100%	🟢
air-quality-backend/src/air_quality/database/forecasts.py	100%	🟢
TOTAL	100%	🟢

updated for commit: 60a9331 by action🐍