return immutable continuous view to this whole nbuff.
Data copy:
We can avoid data copy if this nbuff store single immutable chunk. Then we just return ref to this chunk
We can't avoid data copy if nbuff span several chunks. Then we have to join them.
return immutable continuous view to this whole nbuff. Data copy: We can avoid data copy if this nbuff store single immutable chunk. Then we just return ref to this chunk We can't avoid data copy if nbuff span several chunks. Then we have to join them.