feat(assets): align Facebook AdsStats with CampaignsStats, allow BigQuery field addition under RECONCILE

[aaaaahaaaaa]

What

Two commits, in the order they must land:

1. fix(google-cloud): BigQuery loads may add declared columns under RECONCILE. One helper decides schema_update_options for both load paths (Parquet DataFrame and JSON rows). It returns ALLOW_FIELD_ADDITION only when the destination's materialization strategy is RECONCILE and a declared schema drives the load. AUTO/STRICT are unchanged; schema-less loads never let inferred columns grow a table.
2. feat(assets): Facebook AdsStats aligned with CampaignsStats. AdsStats grows from 75 to 200 fields (the 122 action-type columns CampaignsStats already declares, copied verbatim, plus attribution_setting, quality_ranking, converted_product_quantity). CampaignsStats gains the same three scalars (193 to 196). Existing fields, order and style untouched.

Why

Both Facebook stats assets request the same actions / action_values / cost_per_action_type / unique_actions arrays from Meta; the pivot yields one column per action type and the schema is the allowlist the RECONCILE step keeps. With 75 declared columns, purchase, add_to_cart, initiate_checkout, view_content, search and the omni / onsite_web / pixel breakdowns were fetched and silently dropped at ad level. The 75-vs-193 gap dates from how the two schemas were sampled in April 2024, not from any API or size constraint (identical requests, sparse columns cost roughly 8 % per row).

Widening a schema was not releasable before the first commit: the load job carries the declared schema with WRITE_APPEND and no schema_update_options, so an existing table rejects the first append with "Cannot add fields".

Verification

• TestSchemaParity (assets) fails if AdsStats ever lacks a campaign action column or if a requested field is left undeclared; TestSchemaUpdateOptions (google-cloud) covers RECONCILE with and without schema, and AUTO.
• Live ad hoc run against a Swarovski production account (403584573777711) for 2026-08-28, both assets, local destination: rows 26,885 / 2,686, impressions 3,613,356, spend 11,673.22, purchases 704, all identical to the previous stack; 69 newly populated ad-level columns; nothing undeclared in the output.
• ruff check, ty, full pytest via pre-commit on both commits.

Reviewer notes

• Merge with rebase; the fix commit must not land after the feat commit.
• ruff format --check flags two pre-existing hunks in destination.py unrelated to this change; formatting is not enforced by pre-commit, so they were left alone.
• account_id stays str on AdsStats and int on CampaignsStats; changing a type on existing tables is a separate decision.
• Per-account custom conversions (offsite_conversion_custom_<id>) are out of scope of a shared catalog schema.

By Digitl

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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