DuckDB bindings are unsafe

[gatesn]

Specifically, impl Clone for Vector can result in a dangling pointer in the "borrowed" version.

A better way to implement bindings might be:

/// An owned DuckDB vector
struct Vector {
   ptr: *mut duckdb_vector
}

/// A borrowed DuckDB vector
struct VectorRef<'a> {
  ptr: *const duckdb_vector,
  _phantom: PhantomData<&'a ()>,
} 

impl Vector {
   fn as_ref(&self) -> VectorRef<'_> {
      ...
   }
}

impl Drop for Vector {
   fn drop(self) {
     duckdb_free(self.ptr)
   }
}

[gatesn]

Fixed by #6620