refactor(wkt): move _AnyPackable to its own file

packages/wkt/Sources/GoogleCloudWkt/Any.swift

@@ -94,33 +94,3 @@ extension `Any`: _AnyPackable {
   // The JSON field used to store types with custom encoding.
   static internal let valueField = "value"
 }
-
-/// A type conforming to the `_AnyPackable` protocol can be packed into and unpacked from ``Any``.
-public protocol _AnyPackable {
-  static var _anyTypeUrl: String { get }
-  init(fromAny any: `Any`) throws
-  func _pack() throws -> Struct
-}
-
-// Deserializes a message of type `M` from an `Any`.
-public func _slowAnyDeserialize<M: Decodable & _AnyPackable>(
-  _ type: M.Type, from: `Any`
-) throws -> M {
-  if M._anyTypeUrl != from._type {
-    throw AnyError.mismatchedTypeUrl
-  }
-  let encoder = JSONEncoder();
-  encoder.outputFormatting = [.withoutEscapingSlashes]
-  let data = try encoder.encode(from.fields)
-  let decoder = _ProtoJSONDecoder()
-  return try decoder.decode(M.self, from: data)
-}
-
-// Serializes a message of type `M` into an `Any`.
-public func _slowAnySerialize<M: Encodable>(message: M) throws -> Struct {
-  let encoder = JSONEncoder()
-  encoder.outputFormatting = [.withoutEscapingSlashes]
-  let data = try encoder.encode(message)
-  let decoder = _ProtoJSONDecoder()
-  return try decoder.decode(Struct.self, from: data)
-}

packages/wkt/Sources/GoogleCloudWkt/AnyPackable.swift

@@ -0,0 +1,45 @@
+// Copyright 2026 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+import Foundation
+
+/// A type conforming to the `_AnyPackable` protocol can be packed into and unpacked from ``Any``.
+public protocol _AnyPackable {
+  static var _anyTypeUrl: String { get }
+  init(fromAny any: `Any`) throws
+  func _pack() throws -> Struct
+}
+
+// Deserializes a message of type `M` from an `Any`.
+public func _slowAnyDeserialize<M: Decodable & _AnyPackable>(
+  _ type: M.Type, from: `Any`
+) throws -> M {
+  if M._anyTypeUrl != from._type {
+    throw AnyError.mismatchedTypeUrl
+  }
+  let encoder = JSONEncoder();
+  encoder.outputFormatting = [.withoutEscapingSlashes]
+  let data = try encoder.encode(from.fields)
+  let decoder = _ProtoJSONDecoder()
+  return try decoder.decode(M.self, from: data)
+}
+
+// Serializes a message of type `M` into an `Any`.
+public func _slowAnySerialize<M: Encodable>(message: M) throws -> Struct {
+  let encoder = JSONEncoder()
+  encoder.outputFormatting = [.withoutEscapingSlashes]
+  let data = try encoder.encode(message)
+  let decoder = _ProtoJSONDecoder()
+  return try decoder.decode(Struct.self, from: data)
+}