Filter out metered line items from billing schema

This update refines the process of creating a billing schema by filtering out metered line items. The change is necessary as metered line items can be shared across different plans, potentially causing conflicts or duplicates in the schema.

packages/billing/core/src/create-billing-schema.ts

@@ -173,7 +173,12 @@ export const PlanSchema = z
   )
   .refine(
     (item) => {
-      const ids = item.lineItems.map((item) => item.id);
+      // metered line items can be shared across plans
+      const lineItems = item.lineItems.filter(
+        (item) => item.type !== LineItemType.Metered,
+      );
+
+      const ids = lineItems.map((item) => item.id);
 
       return ids.length === new Set(ids).size;
     },