Runner Release 3.1.8

Machine Runner:

• Fixed a regression where task-agent logs were only written to stderr and not to the log file when configured.
• Fixed an issue on Windows where backslashes in file paths were incorrectly stripped during command prefix expansion, causing task execution failures for some command prefixes.
• Fixed a bug where the task-agent binary was re-downloaded even when it already existed in the local cache, causing unnecessary network usage during task execution.
• The machine driver now configures a job object for the task-agent process and its child processes, ensuring they are properly terminated during cleanup.