Consolidate source + remove tests

[fivetran-data-model-bot]

Summary

This PR is to combine the source and transform packages and remove tests not compatible with dbt Fusion 1.10.6+.

Please check the below automated updates were successful:

MANUAL UPDATES

• If applicable, merge in the Q2 FY26 Automatic Package Updates PR.
• If there are 2 docs.md files, consolidate the definitions the file in the main folder and remove the 2nd file.
• Scan the README for non-standard references to the source package and remove or update.
• Copy the passthrough vars or other non-standard vars from the source dbt_project.yml to the transform dbt_project.yml.
• Check BK run logs for at least 2 warehouses
  • No further deprecation warnings
  • No union data "table not found" type warnings
• Make sure below automatic updates were applied correctly.

Source + Transform Consolidation

• Moved models/macros to models/staging/ and macros/staging/.
• Updated all var('') references within models to use ref('stg_snapchat_ads__').
• Updated vars in dbt_project.yml from refs to sources.
• Removed the source package from packages.yml.
• Major version bump to v1.0.0 (or higher if applicable)

dbt Fusion Compatibility

• Removed dbt_utils.unique_combination_of_columns test
• Accepted values tests were removed where applicable (Shopify, NetSuite, QuickBooks).

YAML & Config Updates

• Moved loaded_at_field under config: in src.yml, grouped with freshness
• Added +schema and +materialization for the staging models in dbt_project.yml.

README

• Removed references to the source package in:
  • Overview
  • Installation instructions
  • Dependencies list
  • Schema override examples

[fivetran-avinash]

@fivetran-joemarkiewicz Approved with a few requests (I think Buildkite was passing the staging models as tables already which was why I didn't hold off on approving, but the update should still be made).