[R] Add arrow ExtensionType implementation + S3 methods for Arrow objects

[paleolimbot]

Like the previous geoarrow incarnation, we should provide arrow package integration. This allows direct use of things like arrow::read_parquet() and the arrow package dplyr integration. I think the implementation will be similar in concept ( https://github.com/paleolimbot/geoarrow/blob/master/R/pkg-arrow.R ) but nanoarrow has some helpers to leverage (as_data_type() implementations, etc.).