Modified the download generator in aria2c to track progress by the number of completed segments (len(completed)) when downloading multiple files. Single-file downloads remain byte-based.
When ensure_started() is called while aria2c is already running, it now compares the requested proxy/max_workers against the values the process was started with and logs a warning if they differ (since the running process cannot be reconfigured in-place). Startup no longer uses a fixed sleep; instead it probes the JSON-RPC endpoint with a bounded retry loop (aria2.getVersion) and only proceeds once RPC is responsive, terminating the subprocess and raising on timeout.
- Use singleton _Aria2Manager to reuse one aria2c process via RPC
- Add downloads via aria2.addUri instead of stdin input file
- Track per-GID byte-level progress (completedLength/totalLength)
- Add thread-safe operations with threading.Lock
- Enable graceful cancellation by removing individual downloads via RPC
