If hooks are not unregistered Blender will report a leak on exit.
Store the hooks as unique_ptrs to remove manual memory management and
encapsulate the previous global list inside a function. These changes
ensure that everything is cleaned up on termination.
Also makes a small change to the hook documentation for a missing
`import` statement.
Pull Request: https://projects.blender.org/blender/blender/pulls/118294
9e8bbc1129