Can't pack into std::span

[zanderdk]

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According to the documentation pack_into should be able to pack_into any byte_container, but the function takes a std:array instead of std::span or equivalent. https://github.com/CrustyAuklet/bitpacker/blob/c62dbbf4fe40f267a06c94f3675aaa2579af8cfe/include/bitpacker/bitpacker.hpp#L822

[CrustyAuklet]

thanks for pointing this out! I've been working on a major refactor in the multi-header-2 branch, so I made the fix in a branch off of that. I mainly test with span-lite and this breaks on MSVC right now. I opened up a issue there, and I will see what they say.