Fix discoverability of submodules inside pd.util

[galipremsagar]

Description

Fixes: #17166

This PR fixes the discoverability of the submodules of attributes and modules inside pd.util. Somehow importlib.import_module("pandas.util").__dict__ doesn't display submodules and only root level attributes.

Checklist

• I am familiar with the Contributing Guidelines.
• New or existing tests cover these changes.
• The documentation is up to date with these changes.

[galipremsagar]

/merge

[Matt711]

The errors I'm seeing are

ERROR python/cudf/cudf_pandas_tests/test_array_function.py - AttributeError: module 'pandas.util' has no attribute 'capitalize_first_letter'
ERROR python/cudf/cudf_pandas_tests/test_cudf_pandas.py - AttributeError: module 'pandas.util' has no attribute 'capitalize_first_letter'
ERROR python/cudf/cudf_pandas_tests/test_cudf_pandas_cudf_interop.py - AttributeError: module 'pandas.util' has no attribute 'capitalize_first_letter'
ERROR python/cudf/cudf_pandas_tests/test_cudf_pandas_no_fallback.py - AttributeError: module 'pandas.util' has no attribute 'capitalize_first_letter'
ERROR python/cudf/cudf_pandas_tests/test_profiler.py - AttributeError: module 'pandas.util' has no attribute 'capitalize_first_letter'

which is coming from https://github.com/rapidsai/cudf/blob/branch-24.12/python/cudf/cudf/pandas/module_accelerator.py#L458.

Edit: capitalize_first_letter is not defined in __getattr__ https://github.com/pandas-dev/pandas/blob/2.2.x/pandas/util/__init__.py

[mroeschke]

Noting that there will be discrepancies depending on pandas 2.x version

pandas 2.2 (and upcoming 2.3) will have capitalize_first_letter

pandas 2.0, 2.1 (and upcoming 3.0) will not have capitalize_first_letter

[galipremsagar]

/okay to test