lib/types: add ints.positive.

For values that are positive, but cannot be 0.

lib/tests/modules/declare-int-positive-value.nix

@@ -0,0 +1,9 @@
+{ lib, ... }:
+
+{
+  options = {
+    value = lib.mkOption {
+      type = lib.types.ints.positive;
+    };
+  };
+}

lib/tests/modules/define-value-int-zero.nix

@@ -0,0 +1,3 @@
+{
+  value = 0;
+}