sdk scan should support table semanteme

有用户表示希望tera提供的scan result_stream可以表现得更符合一个表格系统特征：

```
if (result_stream->new_row() ) { //可以替换为next()
for ( item in cells) {
get_data_from_cell();
}
}
```

The issue names no files or tests; start by locating the C++ SDK scan and result_stream implementation and reading how rows and cells are currently exposed. Compare that API with the proposed new_row()/next() iteration and determine the required semantics. Done means scan results support clear row-then-cell traversal, with coverage for the new behavior.

Written by the indexing model from the issue text.