This will be caught by new test cases: when the initial chunk is empty,
a dereference before calling operator++ on the iterator will crash as
the initial chunk's size is never checked.
Previously, although we were taking a moved chunk, we still copied it
into our chunk list. This makes DisjointChunk compatible with containers
that don't have a copy constructor but a move constructor.
This is a raffinement of 49cbd4dcca.
Previously, the container was scanned to compute the size in the unhappy
path. Now, using `all_of` happy and unhappy path should be fast.
DisjointChunks<T> provides a nice interface over multiple sequential
Vector<T>'s, allowing the user to iterate over/index into/slice from
said buffers as if they were a single contiguous buffer.
To work with views on such objects, DisjointSpans<T> is provided, which
has the same behaviour but does not own the underlying objects.
