[FIX] Update rate limiter acquire method and fix circular imports

Improves rate limiter behavior and resolves test failures by properly
implementing burst limit checks in acquire(). Fixes circular dependency
by moving BCRAApiError to a dedicated exceptions module.

 - Updates acquire() to correctly handle burst limits and delays
 - Creates exceptions.py module to resolve circular imports
 - Ensures consistent rate limiting behavior in tests

src/bcra_connector/__init__.py

@@ -1,5 +1,4 @@
 from .__about__ import __version__
-from .exceptions import BCRAApiError
 from .bcra_connector import BCRAConnector
 from .cheques import Cheque, ChequeDetalle, ChequeResponse, Entidad, EntidadResponse
 from .cheques import ErrorResponse as ChequesErrorResponse
@@ -13,6 +12,7 @@
 )
 from .estadisticas_cambiarias import ErrorResponse as CambiariasErrorResponse
 from .estadisticas_cambiarias import Metadata, Resultset
+from .exceptions import BCRAApiError
 from .principales_variables import DatosVariable, PrincipalesVariables
 from .rate_limiter import RateLimitConfig
 from .timeout_config import TimeoutConfig

src/bcra_connector/bcra_connector.py

@@ -17,10 +17,10 @@
 
 from .cheques import Cheque, Entidad
 from .estadisticas_cambiarias import CotizacionDetalle, CotizacionFecha, Divisa
+from .exceptions import BCRAApiError
 from .principales_variables import DatosVariable, PrincipalesVariables
 from .rate_limiter import RateLimitConfig, RateLimiter
 from .timeout_config import TimeoutConfig
-from .exceptions import BCRAApiError
 
 
 class BCRAConnector:

src/bcra_connector/exceptions.py

@@ -3,4 +3,5 @@
 
 class BCRAApiError(Exception):
     """Custom exception for BCRA API errors."""
+
     pass