Allow user-managed Pool in Wav2Vec2ProcessorWithLM.batch_decode (#18351)
* [Wav2Vec2] Allow user-managed Pool in Wav2Vec2ProcessorWithLM.batch_decode
* [Wav2Vec2] Add user-managed LM's pool tests and usage examples
* Improve styling
Co-authored-by: Sylvain Gugger <35901082+sgugger@users.noreply.github.com>
* [Wav2Vec2] Fix hyperlink references
Co-authored-by: Sylvain Gugger <35901082+sgugger@users.noreply.github.com>