report: multithread write_error_logs, avoid hammering cache.nixos.org

[pbsds]

No description provided.

[pbsds]

Any other inputs @Mic92? @GaetanLepage could you also have a look?

[GaetanLepage]

This looks like a very good idea!
Have you tested it?
I was wondering if the injection of substituters in the CLI arguments was working.
Shouldn't there be additional quotes around the list of substituters.

[pbsds]

I've tested that --option substituters "" causes nix log to fail to retrieve the build log if it is not in the local store. subprocess.run does not go through any shell, so no additional escaping is needed. I've also been using this on my big-parallel builder when checking larger rebuilds