Add initial Pico-8 cartridges for testing

- Created test_cart.p8 with basic drawing functionality and a print statement.
- Created test_unix.p8 with a simple initialization function.

scripts/types/ExecType.js

@@ -0,0 +1,13 @@
+/**
+ * Type descriptor for execution flow pins.
+ *
+ * @type {import('./TypeRegistry.js').TypeDescriptor}
+ */
+export const ExecType = {
+  id: "exec",
+  label: "Exec",
+  color: "#ffffff",
+  isVariable: false,
+  isLocalVariable: false,
+  defaultValue: null,
+};