Implement Variable-size Binary Layout

Implement read and write of the [Variable-size Binary Layout](https://arrow.apache.org/docs/format/Columnar.html#variable-size-binary-layout) and verify with integration tests.

Start with the Apache Arrow Variable-size Binary Layout specification linked in the issue, then locate the repository's read and write entry points for layouts. Add integration tests covering both operations; done means the implementation conforms to the specified layout and those tests pass.

Written by the indexing model from the issue text.