[BUG] .str should not allow adding any new attribute other than defined

[galipremsagar]

Describe the bug
.str appears to be silently allowing adding new attributes, rather than raising an error.

Steps/Code to reproduce bug

In [1]: import cudf

In [2]: s = cudf.Series(["foo", "bar"])

In [3]: s.str.abc = "a"

In [5]: s.to_pandas().str.abc = "a"
---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
Cell In[5], line 1
----> 1 s.to_pandas().str.abc = "a"

File /datasets/pgali/envs/cudfdev/lib/python3.12/site-packages/pandas/core/base.py:177, in NoNewAttributesMixin.__setattr__(self, key, value)
    166 def __setattr__(self, key: str, value) -> None:
    167     # _cache is used by a decorator
    168     # We need to check both 1.) cls.__dict__ and 2.) getattr(self, key)
    169     # because
    170     # 1.) getattr is false for attributes that raise errors
    171     # 2.) cls.__dict__ doesn't traverse into base classes
    172     if getattr(self, "__frozen", False) and not (
    173         key == "_cache"
    174         or key in type(self).__dict__
    175         or getattr(self, key, None) is not None
    176     ):
--> 177         raise AttributeError(f"You cannot add any new attribute '{key}'")
    178     object.__setattr__(self, key, value)

AttributeError: You cannot add any new attribute 'abc'