[doctest] Fixes

[stevhliu]

Attempts to fix some of the failing doctests 😅

Some of the ones I couldn't figure out:

• CodeLlama is gated and the doctest job can't access it?
• Moshi, not sure what the waveform_to_token_ratio value should be
• SigLIP, FlashAttention2 is not installed so attn_implementation="flash_attention_2" is causing it to fail
• generation_strategies.md, the facebook/layerskip-llama3.2-1B checkpoint is also gated and can't be accessed
• pipeline_tutorial.md and quicktour.md, out-of-memory on the tests?
• task_summary.md, not sure how to resolve RuntimeError('CuDNN error: CUDNN_STATUS_INTERNAL_ERROR')

[ArthurZucker]

part of the changes are caused to updating the default NB of toekns generated to 20 + length of input!