feat: add basic process compose module

lib/modules/process_compose_test.nix

@@ -0,0 +1,28 @@
+{
+  ntlib,
+  devshell,
+  ...
+}: let
+  module = ./process_compose.nix;
+in {
+  suites."Process-Compose" = {
+    pos = __curPos;
+    tests = [
+      {
+        name = "basic";
+        type = "script";
+        script = let
+          shell = devshell.mkShell {
+            imports = [module];
+            process-compose.enable = true;
+          };
+        in
+          # sh
+          ''
+            ${ntlib.helpers.scriptHelpers}
+            assert "-f ${shell}/bin/pc" "/bin/pc should exist"
+          '';
+      }
+    ];
+  };
+}