Add support for not processing files that already exist on remote

[rtibbles]

• Adds support for files that already exist on remote
• Threads validation, processing, and uploading to decrease processing time for ricecooker runs
• Always check/fetch content files on upstream from cloud flared domain, rather than api.
• Adds support for moving the faststart flag to the beginning of a file
• Improve logging for file upload failures
• Ensure file duration is properly coerced to an integer
• Give fallback for file duration extraction when the container cannot be used for file duration metadata