nix(refactor): Add buildToolbox to streamline module interface towards shell.nix

nix/memory.nix

@@ -1,7 +1,7 @@
 # The memory tests have large dependencies (a profiled build of PostgREST)
 # and are run less often than the spec tests, so we don't include them in
 # the default test environment. We make them available through a separate module.
-{ buildEnv
+{ buildToolbox
 , checkedShellScript
 , curl
 , postgrestProfiled
@@ -22,9 +22,8 @@ let
       '';
 
 in
-buildEnv
-  {
-    name = "postgrest-memory";
-
-    paths = [ test.bin ];
-  } // { bashCompletion = test.bashCompletion; }
+buildToolbox
+{
+  name = "postgrest-memory";
+  tools = [ test ];
+}