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

checks/impure/flake-module.nix

@@ -1,5 +1,5 @@
-{ ... }: {
-  perSystem = { pkgs, lib, ... }: {
+{ self, ... }: {
+  perSystem = { pkgs, lib, self', ... }: {
     packages = rec {
       # a script that executes all other checks
       impure-checks = pkgs.writeShellScriptBin "impure-checks" ''
@@ -13,9 +13,86 @@
         ]}"
         ROOT=$(git rev-parse --show-toplevel)
         cd "$ROOT/pkgs/clan-cli"
+        ${self'.packages.vm-persistence}/bin/vm-persistence
         nix develop "$ROOT#clan-cli" -c bash -c "TMPDIR=/tmp python -m pytest -m impure ./tests $@"
       '';
 
+      # TODO: port this to python and make it pure
+      vm-persistence =
+        let
+          machineConfigFile = builtins.toFile "vm-config.json" (builtins.toJSON {
+            clanCore.state.my-state = {
+              folders = [ "/var/my-state" ];
+            };
+            # powers off the machine after the state is created
+            systemd.services.poweroff = {
+              description = "Poweroff the machine";
+              wantedBy = [ "multi-user.target" ];
+              after = [ "my-state.service" ];
+              script = ''
+                echo "Powering off the machine"
+                poweroff
+              '';
+            };
+            # creates a file in the state folder
+            systemd.services.my-state = {
+              description = "Create a file in the state folder";
+              wantedBy = [ "multi-user.target" ];
+              script = ''
+                echo "Creating a file in the state folder"
+                echo "dream2nix" > /var/my-state/test
+              '';
+              serviceConfig.Type = "oneshot";
+            };
+            clan.virtualisation.graphics = false;
+            users.users.root.password = "root";
+          });
+        in
+        pkgs.writeShellScriptBin "vm-persistence" ''
+          #!${pkgs.bash}/bin/bash
+          set -euo pipefail
+
+          export PATH="${lib.makeBinPath [
+            pkgs.coreutils
+            pkgs.gitMinimal
+            pkgs.jq
+            pkgs.nix
+            pkgs.gnused
+            self'.packages.clan-cli
+          ]}"
+
+          clanName=_test_vm_persistence
+          testFile=~/".config/clan/vmstate/$clanName/my-machine/var/my-state/test"
+
+          export TMPDIR=$(${pkgs.coreutils}/bin/mktemp -d)
+          trap "${pkgs.coreutils}/bin/chmod -R +w '$TMPDIR'; ${pkgs.coreutils}/bin/rm -rf '$TMPDIR'" EXIT
+
+          # clean up vmstate after test
+          trap "${pkgs.coreutils}/bin/rm -rf ~/.config/clan/vmstate/$clanName" EXIT
+
+          cd $TMPDIR
+          mkdir ./clan
+          cd ./clan
+          nix flake init -t ${self}#templates.new-clan
+          nix flake lock --override-input clan-core ${self}
+          sed -i "s/__CHANGE_ME__/$clanName/g" flake.nix
+          clan machines create my-machine
+
+          cat ${machineConfigFile} | jq > ./machines/my-machine/settings.json
+
+          # clear state from previous runs
+          rm -rf "$testFile"
+
+          # machine will automatically shutdown due to the shutdown service above
+          clan vms run my-machine
+
+          set -x
+          if ! test -e "$testFile"; then
+            echo "failed: file "$testFile" was not created"
+            exit 1
+          fi
+        '';
+
       runMockApi = pkgs.writeShellScriptBin "run-mock-api" ''
         #!${pkgs.bash}/bin/bash
         set -euo pipefail