Channel-level reporting for Performance Max became available in the API with v23

Starting with v23 the ad_network_type segment returns specific channels (Search, Search Partners, Gmail, YouTube, Display, Discover, Maps) for Performance Max at campaign, asset group and asset level instead of MIXED; asset group-level channel data is API-exclusive and available for dates from June 1, 2025.

Works with the v22 segments ad_using_product_data and ad_using_video. Reporting systems must handle the new enum values instead of the generic MIXED result.