fix(billing): validate quantity parameters and harden quota calculations

Bound user-supplied count/duration parameters at request validation,
route ratio multipliers through guarded setters, and use saturating
int conversions in all quota math paths.

relay/channel/task/ali/adaptor.go

@@ -456,8 +456,10 @@ func (a *TaskAdaptor) EstimateBilling(c *gin.Context, info *relaycommon.RelayInf
 		return nil
 	}
 
+	// metadata can override Duration past standard request validation;
+	// cap it because it is used as a billing multiplier.
 	otherRatios := map[string]float64{
-		"seconds": float64(aliReq.Parameters.Duration),
+		"seconds": float64(min(aliReq.Parameters.Duration, relaycommon.MaxTaskDurationSeconds)),
 	}
 	ratios, err := ProcessAliOtherRatios(aliReq)
 	if err != nil {