add `std` feature to newly added dependency in contracts pallet (#5801)

* remove unnecessary re-export

* enable unleash

* Revert "enable unleash"

This reverts commit 30f11d7befea904d5e9c8c117a1b79eb3e184150.

* Revert "remove unnecessary re-export"

This reverts commit 74229f99587d1e17985b5e7f656f70d32b0e9ebe.

* fix missing std def

* Revert "Revert "enable unleash""

This reverts commit 323fb913c38c8f1ac7424dd22e5f918ff6a0b596.

* Revert "Revert "Revert "enable unleash"""

This reverts commit 3f199674ae024edc32a2ab7ce3a15013d2b285a1.