Cross-runtime consistency fixes

Compara contract_event_handler.py, contract_status_changed_event_handler.py y publication_evaluation_event_handler.py con los runtimes de Java, TypeScript y .NET. Revisa primero los comportamientos indicados de marcas de tiempo, DynamoDB, variables de entorno, validación y métricas; después, ejecuta las pruebas del servicio relevantes si están disponibles. Se considera terminado cuando los handlers de Python coinciden con los contratos establecidos entre runtimes, sin escrituras no deseadas ni métricas duplicadas.

Summary

A set of fixes to align the Python runtime with the other runtimes (Java, TypeScript, .NET) for functional equivalence and cross-runtime consistency.

Contracts Service

Timestamp format (contract_event_handler.py)

• create_contract: replaced datetime.now().strftime("%d/%m/%Y %H:%M:%S") with datetime.now(timezone.utc).isoformat() for both contract_created and contract_last_modified_on
• update_contract: replaced datetime.now().strftime(...) with datetime.now(timezone.utc).isoformat()
• Format change: custom DD/MM/YYYY HH:MM:SS → ISO 8601 YYYY-MM-DDTHH:MM:SS.ffffff+00:00
• Uses the non-deprecated timezone-aware API (timezone.utc) instead of datetime.utcnow()

DynamoDB attribute name (contract_event_handler.py)

• update_contract: changed UpdateExpression from "set contract_status=:t, modified_date=:m" to "set contract_status=:t, contract_last_modified_on=:m"
• This corrects a bug where update_contract wrote to a non-existent modified_date attribute instead of the correct contract_last_modified_on attribute used in create_contract

Observability metrics (contract_event_handler.py)

• Added metrics.add_metric(name="ContractCreated", unit=MetricUnit.Count, value=1) to create_contract success path

Approvals Service

Per-invocation timestamp (contract_status_changed_event_handler.py)

• Removed module-level now = datetime.now() and current_date variable assignments
• Moved timestamp computation inside the handler function body to ensure each invocation captures its own execution time rather than the container initialisation time

Environment variable error type (contract_status_changed_event_handler.py)

• Replaced raise InternalServerError(...) with raise EnvironmentError(...) for both SERVICE_NAMESPACE and CONTRACT_STATUS_TABLE missing variable checks
• Removed the now-unused InternalServerError import from aws_lambda_powertools.event_handler.exceptions

Web Service

Evaluation result validation (publication_evaluation_event_handler.py)

• Added validation guard: only updates DynamoDB when evaluation_result is "APPROVED" or "DECLINED" (case-insensitive)
• Logs a warning and returns without writing to DynamoDB for any other value

Metric name correction (publication_evaluation_event_handler.py)

• Removed duplicate metrics.add_metric(name="PropertiesAdded", ...) call
• Retained metrics.add_metric(name="PropertiesApproved", ...) as the single metric for this path