feat: 算力引擎 Go 后端核心（new-api）

- 统一 OpenAI 兼容 /v1 中继 + 渠道/额度/令牌/流水
- 各领域包：relay 模型网关、model 数据层、controller 管理 API

setting/billing_setting/tiered_billing.go

@@ -0,0 +1,106 @@
+package billing_setting
+
+import (
+	"fmt"
+
+	"github.com/QuantumNous/new-api/pkg/billingexpr"
+	"github.com/QuantumNous/new-api/setting/config"
+	"github.com/samber/lo"
+)
+
+const (
+	BillingModeRatio      = "ratio"
+	BillingModeTieredExpr = "tiered_expr"
+	BillingModeField      = "billing_mode"
+	BillingExprField      = "billing_expr"
+)
+
+// BillingSetting is managed by config.GlobalConfig.Register.
+// DB keys: billing_setting.billing_mode, billing_setting.billing_expr
+type BillingSetting struct {
+	BillingMode map[string]string `json:"billing_mode"`
+	BillingExpr map[string]string `json:"billing_expr"`
+}
+
+var billingSetting = BillingSetting{
+	BillingMode: make(map[string]string),
+	BillingExpr: make(map[string]string),
+}
+
+func init() {
+	config.GlobalConfig.Register("billing_setting", &billingSetting)
+}
+
+// ---------------------------------------------------------------------------
+// Read accessors (hot path, must be fast)
+// ---------------------------------------------------------------------------
+
+func GetBillingMode(model string) string {
+	if mode, ok := billingSetting.BillingMode[model]; ok {
+		return mode
+	}
+	return BillingModeRatio
+}
+
+func GetBillingExpr(model string) (string, bool) {
+	expr, ok := billingSetting.BillingExpr[model]
+	return expr, ok
+}
+
+func GetBillingModeCopy() map[string]string {
+	return lo.Assign(billingSetting.BillingMode)
+}
+
+func GetBillingExprCopy() map[string]string {
+	return lo.Assign(billingSetting.BillingExpr)
+}
+
+func GetPricingSyncData(base map[string]any) map[string]any {
+	extra := make(map[string]any, 2)
+	if modes := GetBillingModeCopy(); len(modes) > 0 {
+		extra[BillingModeField] = modes
+	}
+	if exprs := GetBillingExprCopy(); len(exprs) > 0 {
+		extra[BillingExprField] = exprs
+	}
+	return lo.Assign(base, extra)
+}
+
+// ---------------------------------------------------------------------------
+// Smoke test (called externally for validation before save)
+// ---------------------------------------------------------------------------
+
+func SmokeTestExpr(exprStr string) error {
+	return smokeTestExpr(exprStr)
+}
+
+func smokeTestExpr(exprStr string) error {
+	vectors := []billingexpr.TokenParams{
+		{P: 0, C: 0, Len: 0},
+		{P: 1000, C: 1000, Len: 1000},
+		{P: 100000, C: 100000, Len: 100000},
+		{P: 1000000, C: 1000000, Len: 1000000},
+	}
+	requests := []billingexpr.RequestInput{
+		{},
+		{
+			Headers: map[string]string{
+				"anthropic-beta": "fast-mode-2026-02-01",
+			},
+			Body: []byte(`{"service_tier":"fast","stream_options":{"include_usage":true},"messages":[1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21]}`),
+		},
+	}
+
+	for _, v := range vectors {
+		for _, request := range requests {
+			result, _, err := billingexpr.RunExprWithRequest(exprStr, v, request)
+			if err != nil {
+				return fmt.Errorf("vector {p=%g, c=%g}: run failed: %w", v.P, v.C, err)
+			}
+			if result < 0 {
+				return fmt.Errorf("vector {p=%g, c=%g}: result %f < 0", v.P, v.C, result)
+			}
+		}
+	}
+	return nil
+}