VMs: persist state folders on host

Done:
- move vm inspect attrs from system.clan.vm.config to clanCore.vm.inspect. This gives us proper name and type checking. everything in `system` is basically freeform, so the previous option definitions were never enforced
- when running VMs, mount state directory from ~/.config/clan/vmstate/{...} from the host to /var/vmstate inside the vm
- create bind mount inside the VM from /var/vmstate/{folder} to / for all folders defined in clanCore.state.<name>.folders

TODOs:
- make sure directories in ~/.config/clan/vmstate never collide (include hash of clan-url, etc.)
- port impure test to python

nixosModules/clanCore/outputs.nix

@@ -45,12 +45,6 @@
           '';
           default = "${pkgs.coreutils}/bin/true";
         };
-        vm.config = lib.mkOption {
-          type = lib.types.attrs;
-          description = ''
-            the vm config
-          '';
-        };
         vm.create = lib.mkOption {
           type = lib.types.path;
           description = ''