Vouch request: add stepfun (step plan) and longcat.ai as a provider

[mintychochip]

Hello,

I am really interested in the project and have been using omp as my daily driver every day for the past 2 weeks.

Currently plan to add both chinese providers:

https://platform.stepfun.ai/step-plan
http://longcat.ai

I have an existing issue for Step Fun #4036

Thank you so much for the harness!