Nix function from string to pseudorandom integer

Or: Load balancing remote builders with pseudorandom numbers. Background1 Nix remote builders are fantastic - a machine reachable by SSH plus a few lines of configuration (and avoiding some footguns), and you got yourself seamless remote builds. The main issue is the network traffic between the builder and client host, but in case that will slow things down, disabling remote builders is usually as simple as adding --builders '' or a similar option to the command. Conversely, --max-jobs 0 forces remote builds. Another issue is when a group of people, each on their own machine, are sharing a pool of builders. Since none of these are aware of each other, and there’s no central scheduling, it’s easy for a build machine to end up as a choke point, having every client asking it for resources before trying the next host in the list. This can delay build start-up. Even worse, if a builder is configured to run more than one job in parallel, it might end up doing that even when other builders…