feat: add simplified methods for get_primitive_object to package root

Now you can import them from path `primitive_type` immediately.

src/primitive_type/__init__.py

@@ -2,7 +2,14 @@
 
 from primitive_type.types import Primitive, PrimitiveMap
 from primitive_type.checker import is_primitive, is_nested_dict
-from primitive_type.converter import get_primitive_object, ConvertError
+from primitive_type.converter import (
+    get_primitive_object,
+    get_str_object,
+    get_int_object,
+    get_float_object,
+    get_bool_object,
+    ConvertError,
+)
 from importlib.metadata import version, PackageNotFoundError
 
 try:
@@ -17,5 +24,9 @@ __all__ = [
     "is_primitive",
     "is_nested_dict",
     "get_primitive_object",
+    "get_str_object",
+    "get_int_object",
+    "get_float_object",
+    "get_bool_object",
     "ConvertError",
 ]