Fix: Resolve pytype --strict-none-binding issue in the api client

[jkppr]

This PR addresses pytype errors raised by the --strict-none-binding flag in the api client Search class. The issue stemmed from self._raw_response being initialized to None and then populated later by _execute_query, leading to potential unsoundness when accessing it directly.

The fix modifies _execute_query to always return a value: a dictionary with the search results if the results are not saved to a file and count=False, the total count if count=True, or None if the results are saved to a file. The to_dict method now calls _execute_query if self._raw_response is None and handles the case where _execute_query returns None (indicating a previous to_file call) by raising a ValueError. This approach avoids the less robust solution of using assertions and ensures that to_pandas and other methods always have a valid dictionary to work with.

A similar issue was fixed in story.py to handle cases where a view block did not have a populated view attribute, preventing a potential error.

These changes improve type safety and robustness in the Search and Story classes.

[tomchop]

If _raw_response contains an empty list (no results) will this still evaluate to True? Why not re-use the is None clause instead? Same comment for L 1113