feat(core): dag_parse parsea continue_on.exit_code + retry_policy (v1.1.0)

DagContinueOn gana el campo ExitCodes []int (codigos de salida tolerados) y el
parser mapea continue_on.exit_code desde el YAML. retry_policy (limit,
interval_sec) ya existia en el modelo y ahora queda documentado como contrato
estable para los executors.

Funcion pura: solo normaliza el YAML al modelo DagDefinition; la interpretacion
(reintentar, tolerar codigos) vive en el executor que lo consuma (dag_engine).

Test: 'parsea continue_on.exit_code y retry_policy'. Tag de grupo: scheduler.

functions/core/dag_definition.go

@@ -4,6 +4,11 @@ package core
 type DagContinueOn struct {
 	Failure bool
 	Skipped bool
+	// ExitCodes lists exit codes that are tolerated: if the step exits with one
+	// of these non-zero codes, it is treated as a non-failure (the DAG keeps
+	// going and the run is not marked failed). The real exit code is still
+	// recorded. Empty means only exit 0 is a success (unless Failure is set).
+	ExitCodes []int
 }
 
 // DagRetryPolicy configures automatic retries for a step.