optimize dependences

[liunux4odoo]

Why are these changes needed?

as suggested by #2045, #2129, it would be better to make some dependences optional for different service scenarios.

this pr suppose fastchat will be used in 3 different ways:

1. a controller and openai api server, no torch is required.
2. a model_woker as a LLM api server, torch is required.
3. the user need a web interface built by gradio in addition to the api server.

both of torch and gradio require a large installation capacity. It is efficient for distributed installations to make them optional.

Related issue number (if applicable)

#2045, #2129

Checks

• I've run format.sh to lint the changes in this PR.
• I've included any doc changes needed.
• I've made sure the relevant tests are passing (if applicable).