fix(bigquery): Prefer query over table in get_table_query_string by Jwrede · Pull Request #6360 · feast-dev/feast

When both `table` and `query` are set on a BigQuerySource,
`get_table_query_string()` now returns the query (wrapped in parens)
instead of the table reference. This allows PushSource users to
provide a custom read query (e.g. for deduplication) while keeping
`table` for offline writes via `offline_write_batch()`.

Also applies the same priority inversion to
`get_table_column_names_and_types()` so schema inference matches the
actual read path.

Closes feast-dev#6200

Signed-off-by: Jonathan Wrede <wrede.jonathan00@gmail.com>

The validation only enforces at least one of table/query, not exactly
one. Update the docstring to document the supported behavior when both
are set.

Signed-off-by: Jonathan Wrede <wrede.jonathan00@gmail.com>