Remove intermediate JSON serialization and `rawInput`/`rawOutput` options

Remove intermediate JSON serialization and `rawInput`/`rawOutput` options

Previously, each row was JSON serialized and deserialized on each `.pipeThrough`. The intent of this serialization was to normalize the data of each row, with an escape hatch in the `rawInput` and `rawOutput` options.

However, this approach is counterintuitive because most users would expect a CSV row to simply be an `Array<string>`, NOT a `string` that can be `JSON.parse`-ed into an `Array<string>`. Furthermore, this excessive serialization has a significant performance impact. Lastly, the `rawInput` and `rawOutput` options effectively made `CSVTransformer` an overly complex and difficult-to-use JSON parser on top of a CSV transformer.

So, simply removing the JSON serialization and directly enqueuing the actual object (i.e., the `Array<string>`) resolves all these issues with minimal impact to the user-facing API.