chore: move __c_cpp/* to __ffi

__ffi/c_export/call_in_c.c

@@ -0,0 +1,9 @@
+#include <stdint.h>
+#include <stdio.h>
+
+int32_t count_substrings(const char* value, const char* substr);
+
+int main() {
+    printf("%d\n", count_substrings("banana", "na"));
+    return 0;
+}