Refactor code style and improve documentation

- Standardized string quotes to single quotes across all files.
- Added docstrings to several functions and classes for better clarity.
- Updated mypy configuration in pyproject.toml for enhanced type checking.
- Ignored specific linting rules for test files in ruff configuration.
- Improved error messages in exception handling for better user feedback.
- Cleaned up code formatting and structure for consistency.

tests/test_api.py

@@ -14,50 +14,48 @@ def _build_valid_session_validation(path: Path) -> SessionValidation:
 
 
 def test_download_returns_binary_mp4(monkeypatch: pytest.MonkeyPatch, tmp_path: Path) -> None:
-    expected_content = b"mp4-binary-content"
+    expected_content = b'mp4-binary-content'
 
     def fake_validate_session_file(path: Path) -> SessionValidation:
         return _build_valid_session_validation(path)
 
     def fake_download_video(*, url: str, output_dir: Path, session_path: Path) -> Path:
         del url, session_path
-        downloaded_file = output_dir / "video.mp4"
+        downloaded_file = output_dir / 'video.mp4'
         downloaded_file.write_bytes(expected_content)
         return downloaded_file
 
-    monkeypatch.setattr(api, "validate_session_file", fake_validate_session_file)
-    monkeypatch.setattr(api, "download_video", fake_download_video)
+    monkeypatch.setattr(api, 'validate_session_file', fake_validate_session_file)
+    monkeypatch.setattr(api, 'download_video', fake_download_video)
 
     downloaded_video = api.download(
-        "https://youtube.com/shorts/example",
-        session_path="cookies.txt",
+        'https://youtube.com/shorts/example',
+        session_path='cookies.txt',
     )
 
     assert downloaded_video == DownloadedVideo(
-        filename="video.mp4",
+        filename='video.mp4',
         content=expected_content,
     )
 
 
-def test_download_to_path_returns_path_from_downloader(
-    monkeypatch: pytest.MonkeyPatch, tmp_path: Path
-) -> None:
-    expected_path = tmp_path / "video.mp4"
+def test_download_to_path_returns_path_from_downloader(monkeypatch: pytest.MonkeyPatch, tmp_path: Path) -> None:
+    expected_path = tmp_path / 'video.mp4'
 
     def fake_validate_session_file(path: Path) -> SessionValidation:
         return _build_valid_session_validation(path)
 
     def fake_download_video(*, url: str, output_dir: Path, session_path: Path) -> Path:
         del url, session_path
-        expected_path.write_bytes(b"mp4")
+        expected_path.write_bytes(b'mp4')
         return output_dir / expected_path.name
 
-    monkeypatch.setattr(api, "validate_session_file", fake_validate_session_file)
-    monkeypatch.setattr(api, "download_video", fake_download_video)
+    monkeypatch.setattr(api, 'validate_session_file', fake_validate_session_file)
+    monkeypatch.setattr(api, 'download_video', fake_download_video)
 
     downloaded_path = api.download_to_path(
-        "https://youtube.com/shorts/example",
-        session_path="cookies.txt",
+        'https://youtube.com/shorts/example',
+        session_path='cookies.txt',
         output_dir=tmp_path,
     )
 
@@ -66,15 +64,15 @@ def test_download_to_path_returns_path_from_downloader(
 
 def test_download_rejects_invalid_url() -> None:
     with pytest.raises(InvalidUrlError):
-        api.download("https://example.com/watch?v=1", session_path="cookies.txt")
+        api.download('https://example.com/watch?v=1', session_path='cookies.txt')
 
 
 def test_download_rejects_invalid_session(monkeypatch: pytest.MonkeyPatch) -> None:
     def fake_validate_session_file(path: Path) -> SessionValidation:
         del path
-        return SessionValidation(False, False, False, False, "bad session")
+        return SessionValidation(False, False, False, False, 'bad session')
 
-    monkeypatch.setattr(api, "validate_session_file", fake_validate_session_file)
+    monkeypatch.setattr(api, 'validate_session_file', fake_validate_session_file)
 
-    with pytest.raises(InvalidSessionError, match="bad session"):
-        api.download("https://youtube.com/shorts/example", session_path="cookies.txt")
+    with pytest.raises(InvalidSessionError, match='bad session'):
+        api.download('https://youtube.com/shorts/example', session_path='cookies.txt')