fix: Remove redundancies

Author: n0nSmoker

README.md

@@ -145,7 +145,7 @@ If you want to apply custom serialization logic to specific columns:
 result = item.to_dict(serialize_columns={
     'password': lambda v: '***' if v else None,
     'email': lambda v: v.lower() if v else None,
-    'id': lambda v: str(v),
+    'id': str,
 })
 
 # Set default for all instances of a model

tests/test_serialize_columns.py

@@ -6,7 +6,7 @@ def test_serialize_columns_class_level(get_instance):
 
     class ClassLevelCustomFlatModel(FlatModel):
         serialize_columns = {
-            "id": lambda v: str(v),
+            "id": str,
             "string": lambda v: v.upper() if v else None,
         }
 
@@ -220,7 +220,7 @@ def test_serialize_columns_with_multiple_fields(get_instance):
 
     data = i.to_dict(
         serialize_columns={
-            "id": lambda v: str(v),
+            "id": str,
             "string": lambda v: v.upper() if v else None,
             "bool": lambda v: "YES" if v else "NO",
         }