fix: Ensure nanoarrow.hpp compiles on gcc 4.8

[paleolimbot]

Apparently gcc4.8 takes issue with the use of braces in some places and does not provide is_trivially_copyable() or std::size() 🤷

Closes #462 .

Tested via

export NANOARROW_PLATFORM=centos7
export NANOARROW_ARCH=arm64  # because I'm on MacOS M1
docker compose run --rm verify