Exactly requires c++17 and higher

[b6675]

There is marked with cpp14, but project requires cpp17 at least scoped_lock, template<auto N, ...> if constexpr, std::apply do not let downscale requirements msvc 19 at least c++17 gcc 12 at least c++20 with warning meantioned https://github.com/tripleslash/rocket/issues/8#issue-701518650 clang 15 at least c++20