Optimize ST_AsGeoJSON using `encode_geometry()`

[petern48]

We can do this in a follow-up PR and not this one; however, this chain of WKB bytes -> Wkb object -> GeoTypes geometry -> GeoJSON geometry is probably very slow. If we can use:

https://github.com/geoarrow/geoarrow-rs/blob/e17e9e48a6e1b357d5c71839dd33c7cb72d853c0/rust/geoarrow-geojson/src/encoder/geometry.rs#L31-L48

(which should operate directly on a Wkb object), then I think we might be able to make this quite a bit faster (and support Z values).

Originally posted by @paleolimbot in #469 (comment)

[paleolimbot]

Thank you for converting this to an issue!

While it's fresh, we may also want to consider the output precision compatibility here (i.e., 1.0 vs 1). This probably doesn't affect real-world cases much (not sure how many integer rounded coordinates there are in the wild).