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• #29119 (refactor: Use std::span over Span by maflcko)

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_{Debug: https://github.com/bitcoin/bitcoin/runs/20620445160}

Fixed libc++ CIs

Can we split the fixes from the C++20 stuff? The latter shouldn't be backported...

While it is safe to backport, I don't anything should be backported, unless there is a reason and need. A missing (default) constructor, if it was needed, would result in a compile failure. Given that the previous releases compile, this is not needed. Similar arguments can be made for the other commits.

In any case, every commit is already a separate commit, so it is not possible to split further. Anyone is free to backport any or all commits, or none at all.

Could the bitdeque iterator also get std::contiguous_iterator_tag?

No. As opposed to std::vector, the elements of a deque are not stored contiguously: typical implementations use a sequence of individually allocated fixed-size arrays, with additional bookkeeping, which means indexed access to deque must perform two pointer dereferences, compared to vector's indexed access which performs only one. (Copied from source: https://en.cppreference.com/w/cpp/container/deque)

Also, even if a deque was contiguous, only bitdeque::Iterator::deque_iterator would be contiguous. Not bitdeque::Iterator, because std::addressof(std::bitset::reference) is deleted.