SourceAndSink Stream?

[laysakura]

Is your feature request related to a problem? Please describe.

A source reader must write to a source stream, and a sink writer must read from a sink writer.
Therefore, we need a passthrough pump when we just want to emit rows into a foreign sink.

graph TB
    fsrc(["any source"]) -- "Source reader (any)" -->
    src[[source_A]] -- Pump: just_passthrough -->
    sink[[sink_A]] -- "Sink writer (any)" -->
    fsink(["any"])

Describe the solution you'd like

graph TB
    fsrc(["any source"]) -- "Source reader (any)" -->
    src_sink[[source_sink_A]] -- "Sink writer (any)" -->
    fsink(["any"])

Describe alternatives you've considered

Additional context