fix cpp restore statistic

[hongzhi-gao]

问题

1. RestorableTsFileIOWriter 在恢复 aligned value chunk 统计时，未结合 value page 的 null-bitmap 过滤空值位置，导致空值位也被错误参与统计更新。
2. 恢复写入时只恢复了 schema，没恢复每个设备已经写到的最大时间戳状态

修复内容

1. 修改 cpp/src/file/restorable_tsfile_io_writer.cc. 在恢复 aligned value page 时解析 num_values + null-bitmap按 bitmap 判断当前时间位是否有值，仅对非空位执行 value 解码和统计更新
2. 在 MeasurementSchemaGroup 增加设备级 last_time_（初始 INT64_MIN）。恢复初始化(TsFileWriter::init(RestorableTsFileIOWriter*)) 时：遍历恢复出的 ChunkMeta，从统计信息 end_time_ 回填该设备 last_time_

English Version

Issues

1. In RestorableTsFileIOWriter, aligned value-chunk statistics recovery did not correctly account for the value-page null bitmap, so null positions could be mistakenly included in statistic updates.
2. During recovery append, only schema was restored; the per-device maximum written timestamp state was not restored.

Fixes

1. Updated cpp/src/file/restorable_tsfile_io_writer.cc:

   • When recovering aligned value pages, parse num_values + null-bitmap.
   • Use the bitmap to determine whether each timestamp position actually has a value.
   • Decode value data and update statistics only for non-null positions.

2. Added device-level last_time_ to MeasurementSchemaGroup (initialized to INT64_MIN):

   • In recovery initialization (TsFileWriter::init(RestorableTsFileIOWriter*)), iterate recovered ChunkMeta entries.
   • Rebuild each device’s last_time_ from chunk statistics (end_time_).