Extract POSItemIdentifier to its own file

This prevents the generated code from importing PagedItems from networking.

Author: joshheald

Modules/Sources/Yosemite/PointOfSale/Items/POSItemIdentifier.swift

@@ -0,0 +1,20 @@
+import Foundation
+import Codegen
+
+public struct POSItemIdentifier: Hashable, Sendable, GeneratedCopiable, GeneratedFakeable {
+    public let underlyingType: UnderlyingType
+    public let itemID: Int64
+
+    public init(underlyingType: UnderlyingType, itemID: Int64) {
+        self.underlyingType = underlyingType
+        self.itemID = itemID
+    }
+
+    public enum UnderlyingType: Sendable, GeneratedCopiable, GeneratedFakeable {
+        case product
+        case variation
+        case coupon
+        case loading
+        case error
+    }
+}

Modules/Sources/Yosemite/PointOfSale/Items/PointOfSaleItemServiceProtocol.swift

@@ -1,6 +1,5 @@
 import Foundation
-import Networking
-import Codegen
+import struct Networking.PagedItems
 
 public enum POSItem: Equatable, Identifiable, Hashable {
     case simpleProduct(POSSimpleProduct)
@@ -22,24 +21,6 @@ public enum POSItem: Equatable, Identifiable, Hashable {
     }
 }
 
-public struct POSItemIdentifier: Hashable, Sendable, GeneratedCopiable, GeneratedFakeable {
-    public let underlyingType: UnderlyingType
-    public let itemID: Int64
-
-    public init(underlyingType: UnderlyingType, itemID: Int64) {
-        self.underlyingType = underlyingType
-        self.itemID = itemID
-    }
-
-    public enum UnderlyingType: Sendable, GeneratedCopiable, GeneratedFakeable {
-        case product
-        case variation
-        case coupon
-        case loading
-        case error
-    }
-}
-
 /// POSOrderableItem extends a displayable item with the functions required for using it in an order.
 /// This currently includes adding it, and checking whether it's already in an order.
 /// This may need to become less specific in future, e.g. we currently convert it to a product input, but