Array#pack does not support :buffer kwarg

[segiddins]

It has been supported since at least MRI 3.0 (https://docs.ruby-lang.org/en/3.0/Array.html#method-i-pack), and helps avoid transient string allocations when building up nested binary structures

[andrykonchin]

Thank you for reporting the issue! Indeed, the buffer option exists for a long time (probably since Ruby 2.4).