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

relay/common/request_conversion.go

@@ -0,0 +1,23 @@
+package common
+
+import (
+	"github.com/QuantumNous/new-api/relaykit/relayconvert/convmeta"
+	"github.com/QuantumNous/new-api/relaykit/types"
+)
+
+// GuessRelayFormatFromRequest moved to convmeta with the converters; the
+// delegation keeps host callers unchanged.
+func GuessRelayFormatFromRequest(req any) (types.RelayFormat, bool) {
+	return convmeta.GuessRelayFormatFromRequest(req)
+}
+
+func AppendRequestConversionFromRequest(info *RelayInfo, req any) {
+	if info == nil {
+		return
+	}
+	format, ok := GuessRelayFormatFromRequest(req)
+	if !ok {
+		return
+	}
+	info.AppendRequestConversion(format)
+}