Cleanup some NodeLeaf generic boilerplate

Sources/ARTreeModule/ARTree+insert.swift

@@ -28,7 +28,7 @@ extension ARTree {
           fatalError("replace not supported")
         }
 
-        let newLeaf = NodeLeaf.allocate(key: key, value: value, of: Value.self)
+        let newLeaf = Self.allocateLeaf(key: key, value: value)
         var longestPrefix = leaf.longestCommonPrefix(with: newLeaf, fromIndex: depth)
 
         var newNode = Node4.allocate()
@@ -76,7 +76,7 @@ extension ARTree {
           node.partialBytes.shiftLeft(toIndex: prefixDiff + 1)
           node.partialLength -= prefixDiff + 1
 
-          let newLeaf = NodeLeaf.allocate(key: key, value: value, of: Value.self)
+          let newLeaf = Self.allocateLeaf(key: key, value: value)
           newNode.addChild(forKey: key[depth + prefixDiff], node: newLeaf)
           ref?.pointee = newNode.rawNode
           return true
@@ -86,7 +86,7 @@ extension ARTree {
       // Find next child to continue.
       guard let next = node.child(forKey: key[depth], ref: &ref) else {
         // No child, insert leaf within us.
-        let newLeaf = NodeLeaf.allocate(key: key, value: value, of: Value.self)
+        let newLeaf = Self.allocateLeaf(key: key, value: value)
         node.addChild(forKey: key[depth], node: newLeaf, ref: ref)
         return true
       }

Sources/ARTreeModule/ARTree+utils.swift

@@ -0,0 +1,16 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the Swift Collections open source project
+//
+// Copyright (c) 2023 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See https://swift.org/LICENSE.txt for license information
+//
+//===----------------------------------------------------------------------===//
+
+extension ARTree {
+  static func allocateLeaf(key: Key, value: Value) -> NodeLeaf {
+    return NodeLeaf.allocate(key: key, value: value, of: Value.self)
+  }
+}

Sources/ARTreeModule/NodeLeaf.swift

@@ -10,8 +10,6 @@
 //===----------------------------------------------------------------------===//
 
 struct NodeLeaf {
-  typealias Storage = NodeStorage<Self>
-
   var storage: Storage
 }