feat: add GeozeroGeometry and FromWkb support for postgis_diesel types

[georgeboot]

Summary

• Implements GeozeroGeometry for all postgis_diesel types (Point, PointZ, PointM, PointZM, AnyPoint, LineString<P>, Polygon<P>, MultiPoint<P>, MultiLineString<P>, MultiPolygon<P>, GeometryCollection<P>, GeometryContainer<P>), enabling conversion to any geozero-supported format (GeoJSON, WKT, WKB, SVG, geo-types, etc.)
• Adds PostgisDieselWriter (GeomProcessor) and FromWkb for GeometryContainer<P>, enabling construction of postgis_diesel types from any geozero source
• Adds wkb::Decode<T> / wkb::Encode<T> Diesel FromSql/ToSql impls and impl_diesel_postgis_decode! / impl_diesel_postgis_encode! macros (mirroring existing postgres/sqlx patterns)
• Fully backwards-compatible: existing Ewkb<B> Diesel impls and sql_types are preserved

Motivation

The existing with-postgis-diesel feature only provided raw Ewkb<Vec<u8>> support — opaque WKB bytes with no typed geometry conversion. This meant downstream users had to write hundreds of lines of manual conversion code to bridge postgis_diesel geometries with other formats.

This PR brings the diesel integration to parity with the existing postgres and sqlx integrations, which already have full GeozeroGeometry / FromWkb support via wkb::Encode<T> / wkb::Decode<T>.

Test plan

• 34 unit tests covering all geometry types, dimensions (XY, XYZ, XYM, XYZM), SRID preservation
• Read direction: all postgis_diesel types → WKT and GeoJSON
• Write direction: EWKB roundtrip and GeoJSON → postgis_diesel for Point, PointZ, PointZM, AnyPoint, LineString, Polygon, MultiPoint, MultiLineString, MultiPolygon, GeometryCollection
• cargo clippy clean, cargo test -p geozero passes, all existing tests unaffected
• Compiles with all PostGIS feature combinations (with-postgis-diesel, with-postgis-postgres, with-postgis-sqlx)