Refactor geoarrow-expr-geo

[kylebarron]

Perhaps we should try to align it more with the Datafusion API?

So we'll have Area instead of area, plus Area::return_type and Area::process_array? Something like that. Trying to look forward towards having more udfs in more bindings, not just datafusion.

Perhaps we'll vendor something like ColumnarValue into geoarrow-geo to mimic the DataFusion API?

[kylebarron]

We can create a new "experimental" export in the 0.7 release series so that it's non-breaking until 0.8.

The goal here is so that these sort of kernels can be defined once in geoarrow-expr-* and easily reused in either geodatafusion or geopolars, or etc.