chore: update development dependencies and improve test coverage

- Upgraded `pytest-asyncio` to version 1.0 to ensure compatibility with the latest features and improvements.
- Increased the coverage threshold in pytest configuration to 80%, enhancing the quality assurance process.
- Added a new `conftest.py` file to manage shared fixtures and improve test organization.
- Introduced multiple new test files to cover various components, ensuring comprehensive test coverage across the application.
- Updated the `.coverage` file to reflect the latest coverage metrics.

requirements-dev.txt

@@ -1,4 +1,4 @@
 -r requirements.txt
 pytest>=8.0,<9.0
-pytest-asyncio>=0.24,<1.0
+pytest-asyncio>=1.0,<2.0
 httpx>=0.27,<1.0