Export base streamer. (#36500)
* Export base streamer.
Previously, the base streamer class was not exported so the set of available streamers was fixed to 3 streamer classes.
This change makes it so that customers may extend the default base streamer class.
* make fixup
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Co-authored-by: Joao Gante <joaofranciscocardosogante@gmail.com>
Co-authored-by: Joao Gante <joao@huggingface.co>
