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.

duty_teller.egg-info/requires.txt

@@ -9,7 +9,7 @@ icalendar<6.0,>=5.0
 
 [dev]
 pytest<9.0,>=8.0
-pytest-asyncio<1.0,>=0.24
+pytest-asyncio<2.0,>=1.0
 pytest-cov<7.0,>=6.0
 httpx<1.0,>=0.27