Fix iterator, add to_dict method to CoordsInfo

Author: Jesse Grabowski

pymc_extras/statespace/core/properties.py

@@ -61,10 +61,10 @@ def __contains__(self, key: object) -> bool:
         return key in self._index
 
     def __iter__(self) -> Iterator[str]:
-        return iter(self._index)
+        return iter(self.items)
 
     def __len__(self) -> int:
-        return len(self._index)
+        return len(self.items)
 
     def __str__(self) -> str:
         return f"{self.key_field}s: {list(self._index.keys())}"
@@ -146,6 +146,9 @@ def default_coords_from_model(cls, model: Component | PyMCStateSpace) -> Self:
         coords = [Coord(dimension=dim, labels=labels) for dim, labels in dim_to_labels]
         return cls(coords)
 
+    def to_dict(self):
+        return {coord.dimension: coord.labels for coord in self.items if len(coord.labels) > 0}
+
 
 @dataclass(frozen=True)
 class State(Property):