isolated-vm is now available in private servers!
In order to switch your server to this experimental functionality, run npm install with a prerelease tag 3.0.0-beta:npm install screeps@">3.0.0-beta"
Please note that some mods may become non-functional since playerSandbox event is not implemented yet.
It is recommended to set runners_cnt to 1 in your .screepsrc file, since otherwise it will create multiple global environments for each player. There is a new option runner_threads instead which should be set to the number of your CPU cores.