Macro c_destructor 

macro_rules! c_destructor {
    ($fn_name:ident, $c_type:ty) => { ... };
}

Macro to generate C destructor function with pointer registry support

Security

This macro generates a destructor that:

1. Checks if the pointer is null
2. Validates the pointer is registered (prevents double-free)
3. Unregisters the pointer before freeing (prevents use-after-free)