fix: Final attempts to resolve persistent test errors

This commit includes the latest versions of the test files,
reflecting all attempted fixes for errors in:

1.  `test_get_ad_group_bid_modifiers.py`:
    *   Includes the implementation of the `MockAdGroupBidModifierModel`
      custom class, designed to address the `AttributeError` related to
      the `type(obj).pb(obj)` call. This class is intended to provide the
      necessary `pb` class method and `WhichOneof` behavior.

2.  `test_add_smart_campaign.py`:
    *   Includes extensive refactoring of `client.get_type` mocking
      to provide specifically structured mock objects for
      `SmartCampaignSuggestionInfo` (with list-based iterables for
      `locations` and `ad_schedules`) and `KeywordTheme` (using a
      factory to create `spec`-ed instances with `oneof` fields
      initialized to `None`). These changes were aimed at resolving
      the "argument of type 'MagicMock' is not iterable" and
      "malformed KeywordTheme" errors.

Despite these efforts, you've indicated these errors may still
persist. This provides the current state for your local
investigation, particularly for the 'pb' error.

Author: google-labs-jules[bot]