Currently, each call to the hashing functions sha256, sha512, and hash160 creates a new workspace by using stack-pointer. This leads to inefficient memory usage.

More critically, it introduces the potential for memory-related bugs when a hashing function is used inside a function that is invoked via contract-call?.

To resolve this, each hashing function should allocate its workspace once, store the location in a OnceCell, and reuse it across subsequent calls.