Support built-in `reversed()` on `PaginatedList` (#3260)

Since `PaginatedList` can already be used as in iterator and there is an
interface defined for reversing the list, it makes sense to also
implement the `__reversed__` “dunder” method that is utilized by
`reversed()` built-in function for reversing iterators.

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Signed-off-by: Matej Focko <me@mfocko.xyz>
Co-authored-by: Enrico Minack <github@enrico.minack.dev>