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/dummy_config.py

@@ -0,0 +1,19 @@
+import os
+
+
+class DummyConfig:
+    """Small test configuration object used by unit and integration tests.
+
+    Adjust attributes via environment variables where appropriate.
+    """
+    yt_dlp_path = os.getenv("YTDLP_PATH", "yt-dlp")
+    ffmpeg_path = os.getenv("FFMPEG_PATH", "ffmpeg")
+    aria2c_path = os.getenv("ARIA2C_PATH", "aria2c")
+    max_parallel_downloads = int(os.getenv("TEST_MAX_PARALLEL", "2"))
+    aria2c_connections = int(os.getenv("TEST_ARIA2C_CONN", "2"))
+    download_mode = os.getenv("TEST_DOWNLOAD_MODE", "audio")
+    max_video_quality = os.getenv("TEST_MAX_VIDEO_QUALITY", "1080p")
+    # runtime flags
+    debug = False
+    non_interactive = False
+    prune = False