Rust: Wrap Key instead of extending it
Rust: Wrap Key instead of extending it

- The previously used Box<Key> is unsafe according
to the documentation, since it is not a Rust allocated
struct
- Use a NonNull<elektra_sys::Key> instead and wrap it in a
"Rust-owned" struct
- Therefore the custom bindings that were written and the
Drop implementation can be removed again

mpranj/libelektra,mpranj/libelektra,mpranj/libelektra,mpranj/libelektra,petermax2/libelektra,mpranj/libelektra,mpranj/libelektra,BernhardDenner/libelektra,petermax2/libelektra,petermax2/libelektra,petermax2/libelektra,petermax2/libelektra,BernhardDenner/libelektra,mpranj/libelektra,BernhardDenner/libelektra,BernhardDenner/libelektra,mpranj/libelektra,ElektraInitiative/libelektra,ElektraInitiative/libelektra,petermax2/libelektra,BernhardDenner/libelektra,ElektraInitiative/libelektra,ElektraInitiative/libelektra,mpranj/libelektra,petermax2/libelektra,mpranj/libelektra,ElektraInitiative/libelektra,ElektraInitiative/libelektra,petermax2/libelektra,mpranj/libelektra,petermax2/libelektra,ElektraInitiative/libelektra,ElektraInitiative/libelektra,BernhardDenner/libelektra,BernhardDenner/libelektra,BernhardDenner/libelektra,ElektraInitiative/libelektra,ElektraInitiative/libelektra,ElektraInitiative/libelektra,BernhardDenner/libelektra