fix(tests): Correct and Enhance Tests for Type Helpers

[pankaj-bind]

This pull request addresses incomplete test coverage for the is_dict_of and is_list_of utility functions in tests/types/test_type_helpers.py. The existing tests did not account for several edge cases, including empty inputs, None values, and nested data structures.

The original test suite also contained a failing test for nested dictionaries based on an incorrect assumption about the is_dict_of function's behavior.