chore: checkpoint before Python removal

vendor/pin-project/examples/not_unpin.rs

@@ -0,0 +1,19 @@
+// SPDX-License-Identifier: Apache-2.0 OR MIT
+
+// See ./not_unpin-expanded.rs for generated code.
+
+#![allow(dead_code)]
+
+use pin_project::pin_project;
+
+#[pin_project(!Unpin)]
+struct Struct<T, U> {
+    #[pin]
+    pinned: T,
+    unpinned: U,
+}
+
+fn main() {
+    fn _is_unpin<T: Unpin>() {}
+    // _is_unpin::<Struct<(), ()>>(); //~ ERROR `std::marker::PhantomPinned` cannot be unpinned
+}