Consider switching flatbuffers' dependency by planus

[jorgecarleitao]

flatbuffers (the rust implementation, not the format) has been giving us quite an amount of maintenance burden due to its usage of unsafe and general un-maintainanability (see some of the issues on the rust-advisory list as well as https://github.com/google/flatbuffers/issues).

This issue tracks investigations to migrate to planus. It was recently released and addresses the aformentioned issues with a simpler and easier to follow architecture.

If such switch happens, it is expected to be backward compatible, incur no performance cost, and will make this crate safer.

• https://github.com/DataEngineeringLabs/arrow-format/tree/planus tracks this movement on the arrow-format crate,
• https://github.com/jorgecarleitao/arrow2/tree/planus tracks this movement here

The current status is that I was able to generate the flatbuffers and have it compile, and I am now evaluating the changes required on this end of things (against that branch).

I am aiming at having all tests pass under this change. We can then benchmark the differences and make a decision based on data (maintenance vs performance vs security).

cc @TethysSvensson

[jorgecarleitao]

Closed by #732