gh-140557: Force alignment of empty `bytearray` and `array.array` buffers (GH-140559)

This ensures the buffers used by the empty `bytearray` and `array.array`
are aligned the same as a pointer returned by the allocator.  This is a
more convenient default for interop with other languages that have
stricter requirements of type-safe buffers (e.g. Rust's `&[T]` type)
even when empty.