v0.42.1

Client fixes

Bug fixes only; VGI protocol and API are unchanged from 0.42.0.

• Parallel table-function scans closed early now shut down cleanly. Closing a Client.table_function generator before the scan finished used to leave its reader threads running. A following Client.stop() could then hang (two readers on one pipe), or a pooled worker abandoned mid-stream could corrupt the next call on it. Each reader now cancels its own stream within one batch, and the generator joins the threads and releases the workers.
• Client.bind accepts secrets, at_unit and at_value, matching table_function. You can now bind a secret-backed function or a versioned table's historical schema.
• Filter Encoding v2 parser: view-typed payloads (string_view, binary_view, list_view) are measured correctly on pyarrow < 19, instead of failing with a raw ArrowTypeError.