Fix missing deepcopy import for event stream operations (#589)

Author: SamRemis

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

@@ -131,7 +131,6 @@ private void generateOperation(PythonWriter writer, OperationShape operation) {
         var outputSymbol = symbolProvider.toSymbol(output);
 
         writer.pushState(new OperationSection(service, operation));
-        writer.addStdlibImport("copy", "deepcopy");
         writer.putContext("input", inputSymbol);
         writer.putContext("output", outputSymbol);
         writer.putContext("plugin", pluginSymbol);
@@ -189,6 +188,7 @@ private void writeSharedOperationInit(PythonWriter writer, OperationShape operat
         writer.addImport("smithy_core.types", "TypedProperties");
         writer.addImport("smithy_core.aio.client", "RequestPipeline");
         writer.addImport("smithy_core.exceptions", "ExpectationNotMetError");
+        writer.addStdlibImport("copy", "deepcopy");
 
         writer.write("""
                 operation_plugins: list[Plugin] = [