Use qualified name as ElementPathKey element name to ensure uniqueness

There might be multiple linkable metrics available for a given metric_name + entity_links combo. This is because there might be multiple options for entity paths in the metric subquery, which is not accounted for here. Using the qualified name ensures we will have a unique ElementPathKey for each LinkableMetric.

metricflow/model/semantics/linkable_spec_resolver.py

@@ -120,8 +120,14 @@ def element_name(self) -> str:  # noqa: D102
         return self.reference.element_name
 
     @property
-    def path_key(self) -> ElementPathKey:  # noqa: D102
-        return ElementPathKey(element_name=self.element_name, entity_links=self.join_path.entity_links)
+    def path_key(self) -> ElementPathKey:
+        """Key that can uniquely identify an element and the joins used to realize the element.
+
+        Use qualified name to guarantee uniqueness.
+        """
+        return ElementPathKey(
+            element_name=self.as_group_by_metric_spec.qualified_name, entity_links=self.join_path.entity_links
+        )
 
     @property
     def reference(self) -> MetricReference:  # noqa: D102
@@ -142,6 +148,15 @@ def metric_subquery_entity_links(self) -> Tuple[EntityReference, ...]:
         metric_subquery = self.join_path.metric_subquery_join_path_element
         return metric_subquery.entity_links + (metric_subquery.join_on_entity,)
 
+    @property
+    def as_group_by_metric_spec(self) -> GroupByMetricSpec:
+        """Convert LinkableMetric to GroupByMetricSpec."""
+        return GroupByMetricSpec(
+            element_name=self.element_name,
+            entity_links=self.join_path.entity_links,
+            metric_subquery_entity_links=self.metric_subquery_entity_links,
+        )
+
 
 @dataclass(frozen=True)
 class LinkableElementSet: