Build processing no longer fails when duplicate jobs run for the same build

A race condition could enqueue two build-processing jobs for the same build at the same time. Both jobs downloaded the build archive to a shared temporary path, so one job could overwrite or delete the archive while the other was still unzipping it. The victim then parsed a truncated file and failed with a spurious invalid log line error. Each job now gets a unique temporary download path, so concurrent processing of the same build is safe and builds are reliably ingested.