Add missing no_std cfg_attr

crates/storage/traits/Cargo.toml

@@ -32,6 +32,7 @@ default = ["std"]
 std = [
     "ink_metadata/std",
     "ink_primitives/std",
+    "ink_prelude/std",
     "scale/std",
     "scale-info/std",
 ]

crates/storage/traits/src/lib.rs

@@ -25,6 +25,8 @@
 //! If at least one of the type's fields occupies its own separate storage cell, it is a
 //! non-[`Packed`] type because it occupies more than one storage cell.
 
+#![cfg_attr(not(feature = "std"), no_std)]
+
 mod impls;
 mod storage;