ref(download): Use download service for objectstore requests - #1928

An attacker-controlled storage URL can serve a tiny zstd/gzip/zlib/zip/CAB payload that fetch_file synchronously inflates into a temporary file after the download timeout has ended. Although output is capped at the default 15GiB, the decompression and subsequent minidump processing have no decompression-specific CPU budget; the outer request timeout cannot preempt this synchronous block, allowing substantial CPU and disk exhaustion on the shared worker pool.