feature/foa fast copy fix

[joaquintides]

Restores boost::unordered_flat_[map|set]'s allocator awareness by restricting std::memcpy-based element copy to std::allocator and allocators without a suitable construct memfun.

[pdimov]

Why are the warning restore pragmas not in reverse order of the suppression ones?

[codecov[bot]]

Codecov Report

Merging #176 (200c0c6) into develop (6be2bf8) will increase coverage by 0.04%. The diff coverage is 99.23%.

:exclamation: Current head 200c0c6 differs from pull request most recent head 91eddba. Consider uploading reports for the commit 91eddba to get more accurate results

Additional details and impacted files

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[joaquintides]

Why are the warning restore pragmas not in reverse order of the suppression ones?

I opted for having those pragmas be mutually exclusive (note the #elifs), hence restore order can't be reverse (some branches are true simultaneously).