chore: import upstream snapshot with attribution

native/zero-c/include/zero_contracts.h

@@ -0,0 +1,20 @@
+#ifndef ZERO_C_ZERO_CONTRACTS_H
+#define ZERO_C_ZERO_CONTRACTS_H
+
+/*
+ * Zero-cost access-effect annotations for C API pointer contracts.
+ *
+ * These macros document the caller/callee contract at the declaration site and
+ * are intentionally empty for C compilers. The contract checker keeps exported
+ * native APIs from accepting unannotated pointer parameters or pointer returns.
+ */
+#define Z_IN
+#define Z_OUT
+#define Z_INOUT
+#define Z_SINK
+#define Z_OPTIONAL
+#define Z_RET_OWNED
+#define Z_RET_BORROWED
+#define Z_RET_OPTIONAL
+
+#endif