Support Qwen models

[flaneur2020]

as described in https://arxiv.org/pdf/2309.16609.pdf

the architectural differences between llama are:

references: https://github.com/ml-explore/mlx-examples/blob/main/llms/mlx_lm/models/qwen.py

[flaneur2020]

#179 had added the qwen2 support, however we can close this issue after the chat template for qwen2 got adjusted