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.

tests/test_config.py

@@ -1,4 +1,6 @@
-"""Tests for config.is_admin and config.can_access_miniapp."""
+"""Tests for config.is_admin, config.can_access_miniapp, and require_bot_token."""
+
+import pytest
 
 import duty_teller.config as config
 
@@ -67,3 +69,18 @@ def test_is_admin_by_phone(monkeypatch):
     assert config.is_admin_by_phone("+7 900 111-11-11") is True
     assert config.is_admin_by_phone("79001234567") is False
     assert config.is_admin_by_phone(None) is False
+
+
+def test_require_bot_token_raises_system_exit_when_empty(monkeypatch):
+    """require_bot_token() raises SystemExit with message about BOT_TOKEN when empty."""
+    monkeypatch.setattr(config, "BOT_TOKEN", "")
+    with pytest.raises(SystemExit) as exc_info:
+        config.require_bot_token()
+    assert "BOT_TOKEN" in str(exc_info.value)
+    assert exc_info.value.code != 0
+
+
+def test_require_bot_token_does_not_raise_when_set(monkeypatch):
+    """require_bot_token() does nothing when BOT_TOKEN is set."""
+    monkeypatch.setattr(config, "BOT_TOKEN", "123:ABC")
+    config.require_bot_token()