[client-v2] Implement Streaming API for Binary formats

### Describe

- handle nullables in one place
- make 2 level abstraction - low level writing data types and columns

No files, tests, or entry points are named. Start by locating the client-v2 binary-format streaming code and existing nullable handling, then map how low-level data types and columns could support the higher-level abstraction. Done means nullable values are handled in one place and the requested two-level streaming design is implemented.

Written by the indexing model from the issue text.