feat: add BigQuery Python functions and BQClient type

Funciones CRUD completas para BigQuery: auth, datasets, tables, queries,
jobs, routines, load/export. Tipo BQClient como wrapper del SDK oficial.

python/functions/bigquery/client.py

@@ -0,0 +1,63 @@
+"""Cliente base para Google BigQuery."""
+
+from dataclasses import dataclass, field
+from google.cloud import bigquery
+from google.oauth2 import service_account
+
+
+@dataclass
+class BQClient:
+    """Cliente para Google BigQuery.
+
+    Attributes:
+        project_id: ID del proyecto GCP.
+        _client: Cliente oficial de BigQuery (interno).
+    """
+    project_id: str
+    _client: bigquery.Client = field(repr=False)
+
+    def close(self) -> None:
+        """Cierra el cliente BigQuery."""
+        self._client.close()
+
+    def __enter__(self):
+        return self
+
+    def __exit__(self, *args):
+        self.close()
+
+
+def bq_auth(project_id: str = "", credentials_path: str = "") -> BQClient:
+    """Autentica contra Google BigQuery.
+
+    Tres modos de autenticacion:
+    1. ADC (Application Default Credentials): sin argumentos, usa gcloud auth
+    2. Service account JSON: con credentials_path
+    3. Proyecto explicito: con project_id (usa ADC para credenciales)
+
+    Args:
+        project_id: ID del proyecto GCP. Vacio = detectar de credenciales.
+        credentials_path: Ruta a archivo JSON de service account. Vacio = ADC.
+
+    Returns:
+        BQClient autenticado listo para usar.
+
+    Raises:
+        google.auth.exceptions.DefaultCredentialsError: Si no hay credenciales configuradas.
+        FileNotFoundError: Si credentials_path no existe.
+
+    Example:
+        >>> client = bq_auth()  # ADC
+        >>> client = bq_auth("my-project")  # ADC con proyecto explicito
+        >>> client = bq_auth(credentials_path="/path/to/sa.json")  # Service account
+    """
+    if credentials_path:
+        creds = service_account.Credentials.from_service_account_file(credentials_path)
+        proj = project_id or creds.project_id
+        client = bigquery.Client(credentials=creds, project=proj)
+    elif project_id:
+        client = bigquery.Client(project=project_id)
+    else:
+        client = bigquery.Client()
+
+    return BQClient(project_id=client.project, _client=client)