Set up NilVM to be available as a service in devenv

[glottologist]

We would like the devnet to be available to developers using devenv.sh by adding

service.nilvm.enable = true;
service.nilvm.environment = "devnet";

or something similar

this is to reduce some of the friction when setting up the SDK toolset

[oceans404]

what would a config look like that enables all nillion devtools (so we also get nada and pynadac, etc)