[hybrid_dev] Hybrid dev branch

[RaymondLi0]

✨ Description

For tracking: Hybrid-SSM dev branch

Outstanding issues

• Missing preprocessing when flash-attn is disabled for vision-encoder. -> KeyError: 'image_encoder_attention_mask' (is an issue to run the tests)
• when vision_encoder.image_break_token is not set, shape-mismatch error in the Multimodal-embedding layer.
• debug-layer-outputs/gradients hangs.