Open Variant Rust

This is a Rust implementation of the Open Variant format. This provides a data structure for semi-structured data (like JSON) that is optimized for OLAP queries.

This is based on the specification and Java implementation hosted in the Apache Spark project. The specification can be found here.

There are three libraries:

1. open-variant: The core library that provides the data structure.
2. (TODO) arrow-open-variant: A library to use variant data as an extension type in Apache Arrow.
3. (TODO) datafusion-functions-variant: A library that provides functions to work with variant data in DataFusion.