Add unit tests for endpoints, data processing, and integration

[lerina07]

What was added

• Unit tests for FastAPI endpoints to verify API routes return expected responses.
• Tests for data processing functions to validate data handling and transformations.
• Integration tests to ensure proper integration with Prometheus and Grafana.

Why it’s useful

• Improves overall code reliability and reduces chances of bugs.
• Makes future development and modifications safer and easier.
• Helps maintain project quality and simplifies debugging.

[AryanSharma9917]

#LGTM