feat(task): add adaptor billing interface and async settlement framework

Add three billing lifecycle methods to the TaskAdaptor interface:
- EstimateBilling: compute OtherRatios from user request before pricing
- AdjustBillingOnSubmit: adjust ratios from upstream submit response
- AdjustBillingOnComplete: determine final quota at task terminal state

Introduce BaseBilling as embeddable no-op default for adaptors without
custom billing. Move Sora/Ali OtherRatios logic from shared validation
into per-adaptor EstimateBilling implementations.

Add TaskBillingContext to persist pricing params (model_price, group_ratio,
other_ratios) in task private data for async polling settlement.

Extract RecalculateTaskQuota as a general-purpose delta settlement
function and unify polling billing via settleTaskBillingOnComplete
(adaptor-first, then token-based fallback).

relay/channel/task/taskcommon/helpers.go

@@ -5,7 +5,10 @@ import (
 	"fmt"
 
 	"github.com/QuantumNous/new-api/common"
+	"github.com/QuantumNous/new-api/model"
+	relaycommon "github.com/QuantumNous/new-api/relay/common"
 	"github.com/QuantumNous/new-api/setting/system_setting"
+	"github.com/gin-gonic/gin"
 )
 
 // UnmarshalMetadata converts a map[string]any metadata to a typed struct via JSON round-trip.
@@ -68,3 +71,25 @@ const (
 	ProgressInProgress = "30%"
 	ProgressComplete   = "100%"
 )
+
+// ---------------------------------------------------------------------------
+// BaseBilling — embeddable no-op implementations for TaskAdaptor billing methods.
+// Adaptors that do not need custom billing can embed this struct directly.
+// ---------------------------------------------------------------------------
+
+type BaseBilling struct{}
+
+// EstimateBilling returns nil (no extra ratios; use base model price).
+func (BaseBilling) EstimateBilling(_ *gin.Context, _ *relaycommon.RelayInfo) map[string]float64 {
+	return nil
+}
+
+// AdjustBillingOnSubmit returns nil (no submit-time adjustment).
+func (BaseBilling) AdjustBillingOnSubmit(_ *relaycommon.RelayInfo, _ []byte) map[string]float64 {
+	return nil
+}
+
+// AdjustBillingOnComplete returns 0 (keep pre-charged amount).
+func (BaseBilling) AdjustBillingOnComplete(_ *model.Task, _ *relaycommon.TaskInfo) int {
+	return 0
+}