BigQuery backtick-quoted identifiers not split into schema and table

When parsing BigQuery SQL, backtick-quoted identifiers like `` `dataset.table` `` are returned as a single table name with `nil` schema, rather than being split into schema and table components.

Example

```sql
SELECT * FROM `my_dataset.my_table`

Current behavior

{:schema nil, :table "my_dataset.my_table"}

Expected behavior

{:schema "my_dataset", :table "my_table"}
```

Context

In BigQuery, backticks are used to quote identifiers, and `dataset.table` is the standard way to reference a fully-qualified table. Unlike standard SQL where a quoted identifier like "foo.bar" would be a single identifier containing a literal dot, BigQuery's backtick quoting preserves the dot as a separator between dataset (schema) and table.

Start by locating the BigQuery SQL parsing code and any existing tests for identifier splitting. Reproduce the example, then verify that a backtick-quoted dataset.table produces separate schema and table values while preserving the expected behavior for other identifiers.

Written by the indexing model from the issue text.