Pre-fix, materialize ran the admin source_query as 'COPY (sql) TO parquet'
through the DuckDB BQ extension session. The extension defaults to the
BQ Storage Read API for bq.<ds>.<tbl> references, which rejects views
('non-table entities cannot be read with the storage API'). The fix
always wraps admin SQL into bigquery_query('<billing>', '<inner>') so
COPY uses the BQ jobs API uniformly for tables and views.
Cost guardrail dry-run now operates on the inner SQL (BQ-native), so
the BQ Python client parses it and the cap engages — pre-fix the dry-run
hit 'Table-valued function not found: bigquery_query' and fail-opened.
