v2025.0203.171022

Fix ASAN failure in `array.rend()`. (#219)

The iterator constructor used `array[index]` to initialize an internal
cached view (necessary so that `operator->` can return a pointer), which
caused pointer arithmetic overflow when `index` was -1 -- as in the case
of `rend()`.

This change uses a checked `array.at(index)` method to get a null view
when `index` is out of bounds.

I considered changing `array[index]` to return a null view for
out-of-bounds indexes, but user code may be inadvertently relying on
that behavior, so I am leaving it out of this bug fix.