Add Support for Meituan Longcat series

[yongtenglei]

Description

Hi, Charm team

I personally really like the Longcat series from Meituan, which is a series of competitive MoE models that respond to requests very quickly with high-quality responses. I have seen that LongCat-Flash-Chat has been integrated by others via OpenRouter, so I wonder if it would be possible to add an official provider to this project.

I have created my own fork and integrated both LongCat-Flash-Chat (works perfectly with ​​crush​​ without issues) and LongCat-Flash-Thinking (requires a mandatory content field in assistantMsg) into catwalk.

Here's a ​​patch​​ for ​​crush​​ to handle this requirement:

If you're interested in integrating the Longcat models into the project officially, please let me know. Thanks again!