fix(arrow/cdata): avoid unsafe.Slice on zero-length pointers - #4

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: actions/checkout@3df4ab11eba7bda6032a0b82a6bb43b11571feac, actions/setup-python@39cd14951b08e74b54015e9e001cdefcf80e669f. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/