feat(notify): 重构通信内核并补齐 stream/bulk/record/transfer 能力

- 引入 LogicalConn/TransportConn 分层，ClientConn 保留兼容适配层
  - 新增 Stream、Bulk、RecordStream 三条数据面能力及对应控制路径
  - 完成 transfer/file 传输内核与状态快照、诊断能力
  - 补齐 reconnect、inbound dispatcher、modern psk 等基础模块
  - 增加大规模回归、并发与基准测试覆盖
  - 更新依赖库

internal/transfer/types.go

@@ -0,0 +1,188 @@
+package transfer
+
+import "time"
+
+type Channel string
+
+const (
+	ControlChannel Channel = "control"
+	DataChannel    Channel = "data"
+)
+
+type Direction uint8
+
+const (
+	DirectionSend Direction = iota
+	DirectionReceive
+)
+
+type State uint8
+
+const (
+	StateInit State = iota
+	StateNegotiating
+	StatePrepared
+	StateActive
+	StatePaused
+	StateCommitting
+	StateVerifying
+	StateDone
+	StateAborted
+	StateFailed
+)
+
+func (s State) Terminal() bool {
+	switch s {
+	case StateDone, StateAborted, StateFailed:
+		return true
+	default:
+		return false
+	}
+}
+
+type Range struct {
+	Offset int64
+	Length int64
+}
+
+type Metadata map[string]string
+
+type TelemetryDelta struct {
+	SourceReadDuration  time.Duration
+	StreamWriteDuration time.Duration
+	SinkWriteDuration   time.Duration
+	SyncDuration        time.Duration
+	VerifyDuration      time.Duration
+	CommitDuration      time.Duration
+	CommitWaitDuration  time.Duration
+	SourceReadCount     int
+	StreamWriteCount    int
+	SinkWriteCount      int
+}
+
+type Descriptor struct {
+	ID        string
+	Direction Direction
+	Channel   Channel
+	Size      int64
+	Checksum  string
+	Metadata  Metadata
+}
+
+type Snapshot struct {
+	ID                  string
+	Direction           Direction
+	Channel             Channel
+	State               State
+	Stage               string
+	LastFailureStage    string
+	Size                int64
+	Checksum            string
+	Metadata            Metadata
+	SentBytes           int64
+	AckedBytes          int64
+	ReceivedBytes       int64
+	InflightBytes       int64
+	RetryCount          int
+	TimeoutCount        int
+	LastError           string
+	SourceReadDuration  time.Duration
+	StreamWriteDuration time.Duration
+	SinkWriteDuration   time.Duration
+	SyncDuration        time.Duration
+	VerifyDuration      time.Duration
+	CommitDuration      time.Duration
+	CommitWaitDuration  time.Duration
+	SourceReadCount     int
+	StreamWriteCount    int
+	SinkWriteCount      int
+	StartedAt           int64
+	UpdatedAt           int64
+	CompletedAt         int64
+}
+
+type Begin struct {
+	TransferID string
+	Channel    Channel
+	Size       int64
+	Checksum   string
+	Metadata   Metadata
+}
+
+type BeginAck struct {
+	TransferID string
+	Accepted   bool
+	NextOffset int64
+	Missing    []Range
+	Error      string
+}
+
+type Resume struct {
+	TransferID string
+}
+
+type ResumeAck struct {
+	TransferID string
+	Accepted   bool
+	NextOffset int64
+	Missing    []Range
+	Error      string
+}
+
+type Commit struct {
+	TransferID string
+	Size       int64
+	Checksum   string
+}
+
+type CommitAck struct {
+	TransferID string
+	Accepted   bool
+	Error      string
+}
+
+type Abort struct {
+	TransferID string
+	Stage      string
+	Offset     int64
+	Error      string
+}
+
+type Segment struct {
+	TransferID string
+	Channel    Channel
+	Offset     int64
+	Payload    []byte
+	Flags      uint32
+}
+
+type Ack struct {
+	TransferID string
+	NextOffset int64
+	Missing    []Range
+	Final      bool
+	Error      string
+}
+
+func normalizeChannel(channel Channel) Channel {
+	if channel == "" {
+		return DataChannel
+	}
+	return channel
+}
+
+func cloneMetadata(src Metadata) Metadata {
+	if len(src) == 0 {
+		return nil
+	}
+	dst := make(Metadata, len(src))
+	for key, value := range src {
+		dst[key] = value
+	}
+	return dst
+}
+
+func cloneSnapshot(src Snapshot) Snapshot {
+	src.Metadata = cloneMetadata(src.Metadata)
+	return src
+}