Fix missing deepcopy import for event stream operations

Author: SamRemis

codegen/core/src/main/java/software/amazon/smithy/python/codegen/ClientGenerator.java

@@ -221,6 +221,7 @@ raise ExpectationNotMetError("protocol and transport MUST be set on the config t
 
     private void generateEventStreamOperation(PythonWriter writer, OperationShape operation) {
         writer.pushState(new OperationSection(service, operation));
+        writer.addStdlibImport("copy", "deepcopy");
         writer.addDependency(SmithyPythonDependency.SMITHY_CORE);
         writer.addDependency(SmithyPythonDependency.SMITHY_AWS_CORE.withOptionalDependencies("eventstream"));
         var operationSymbol = symbolProvider.toSymbol(operation);