Update deprecated mem_ops.h function calls to use std::span-based versions and resolve some TODOs#4783

KaganCanSit wants to merge 1 commit intorandombit:masterrandombit/botan:masterfrom

KaganCanSit:feature-handling-some-todo-messagesKaganCanSit/botan:feature-handling-some-todo-messagesCopy head branch name to clipboard