Add initial `TransformStream` CSVWriter implementation

Add initial `TransformStream` CSVWriter implementation

This change enables users to create a `TransformStream` by doing `new CSVWriter()` instead of always creating an ultimate sink `WritableStream`. This behavior is useful when there is some transformation that must be performed on the CSV data before writing (e.g., compressing into a `.csv.gz` file using `CompressionStream`).