Improve test coverage for medicine, patient, and user routes

Enhance unit test coverage for API routes related to medicine, patient, and user modules to ensure reliability and correctness of backend functionality. The current coverage is below expected levels:

medicine_routes.py → ~56%
patient_routes.py → ~65%
users_routes.py → ~74%

The goal is to increase coverage up to to ~100% by covering all logical branches, edge cases, and error scenarios.

Scope of Work:

Write unit tests using pytest
Improve coverage for medicine, patient, and user routes
Validate responses and status codes
Handle error and edge cases

Expected Outcome:

Increased test coverage (~100%)
Improved backend reliability
Early bug detection
Stable API behavior