Refactor test configurations and enhance testing framework

- Replace TempConfig with DummyConfig across tests for consistency
- Introduce unit tests workflow configuration
- Add pytest configuration for standardized test discovery
- Implement comprehensive tests for config loading and downloader behavior
- Clean up unused temp_config.py and related references

tests/conftest.py

@@ -0,0 +1,9 @@
+import pytest
+
+from tests.dummy_config import DummyConfig
+
+
+@pytest.fixture
+def dummy_config():
+    """Return a fresh DummyConfig instance for tests to customize."""
+    return DummyConfig()