Add `geo-traits` reader implementation

[kylebarron]

We have a new core geo crate: geo-traits! This enables zero-copy vector data interchange throughout the GeoRust ecosystem.

This means that any library out there that accepts geo-traits input will just work with shapefile geometries.

This PR implements these traits on new-types around shapefile geometry types.

Change list

• Traits are implemented on existing types where possible. E.g. traits are implemented on Point{M,Z}, MultiPoint{M, Z}, and PolyLine{M, Z}.
• A new MultiPolygon type is created to wrap a shapefile::Polygon. This is a necessity because geo_traits::PolygonTrait makes a distinction between interior and exterior rings. So a bit of pre-processing is needed to ensure that consumers get constant-time coordinate access.
• A few new public types are necessitated by being the iteration objects from MultiPolygon and Polyline.

Questions

• How to handle the dimension for Z geometry types, since we don't know up front whether they'll have M values or not.

[kylebarron]

I don"t know if checking the NO_DATA for M values is worth doing, maybe we could let that thing to the user (but then it's not clear if that's a good idea)

I think the semantics here are that data producers are expected to produce valid data, so I think we should keep the check for M values.