Refactor downloader and file manager for improved rclone integration and add healthcheck and smoke test options

- Renamed download flags in ContentDownloader for clarity.
- Enhanced FileManager with methods to build upload paths and verify existing files for rclone uploads.
- Updated StreamProcessor to return success status for stream processing.
- Added rclone smoke test and healthcheck functions to validate configuration and tool availability.
- Improved environment variable handling with a utility function.
- Updated TwitchArchive to incorporate new rclone verification and processing logic.
- Added unit tests for new functionality and refactored existing tests for clarity and coverage.

Co-authored-by: Copilot <copilot@github.com>

.dockerignore

@@ -0,0 +1,18 @@
+.git
+.github
+.forgejo
+.vs
+.vscode
+venv*/
+__pycache__/
+*.pyc
+archive/
+dotnet/
+tests/
+.pytest_cache/
+bin/temp/
+bin/ffmpeg
+bin/ffmpeg.exe
+bin/ffprobe
+bin/TwitchDownloaderCLI
+bin/TwitchDownloaderCLI.exe