Add unsafe flag to the engine

[arvid220u]

In the unsafe mode, we would allow things like:

1. pdb

and also remove the things that make code slower for the sake of security like:

1. threads in threads (???? not sure if that's it honestly)

[arvid220u]

See https://github.com/cooljoseph1/battlehack20-minimal, although we probably want to keep the bytecode limits and instrumentation in place because I think the threads are what's causing the big slowdown. I'm still not sure what the threads are used for

[arvid220u]

We could also possibly make the debug flag mean exactly this and have the server run with --debug false. And then if we want the server to show debug outputs we can have another flag. Not sure what the best UI is here