Update list and map generators

Author: jonathan343

codegen/core/src/main/java/software/amazon/smithy/python/codegen/generators/ListGenerator.java

@@ -44,7 +44,7 @@ private void generateSerializer() {
         writer.write("""
                 def $1L(serializer: ShapeSerializer, schema: Schema, value: $2T) -> None:
                     member_schema = schema.members["member"]
-                    with serializer.begin_list(schema) as ls:
+                    with serializer.begin_list(schema, len(value)) as ls:
                         for e in value:
                             ${?sparse}
                             if e is None:

codegen/core/src/main/java/software/amazon/smithy/python/codegen/generators/MapGenerator.java

@@ -46,7 +46,7 @@ private void generateSerializer() {
         // narrowing out the None even though there's an explicit is None check.
         writer.write("""
                 def $1L(serializer: ShapeSerializer, schema: Schema, value: $2T) -> None:
-                    with serializer.begin_map(schema) as m:
+                    with serializer.begin_map(schema, len(value)) as m:
                         value_schema = schema.members["value"]
                         for k, v in value.items():
                             ${?sparse}