model_rpc style improvement

[hnyls2002]

What does this PR do?

• Make the old ModelRpcServer an independent class, with the __init__ function to initialize all the fields, which were initialized in exposed_init_model before.
• Change the thread server

  class ModelRpcService(rpyc.Service):
      exposed_ModelRpcServer = ModelRpcServer

[Qubitium]

I am going to chime on the new format part. The new line expansion format of if args is really redundant and inflates line count with no obvious improvement to readability. Should be used when # of args is > some N due to a standard perhaps. If I pass in 3 args, there is no need for 2 extra lines of code. Perhaps project can standardize on a formatting style using a formatter/linter that everyone can adhere to?

[hnyls2002]

@Qubitium The main intention of this PR is not to expand the arguments into multiple lines, as you mentioned. These changes were actually made by our formatting script

https://github.com/sgl-project/sglang/blob/main/scripts/format.sh

I believe the verdict on when to introduce a new line isn't solely influenced by the number of arguments. Factors such as indentation and the maximum length of a line should also be considered. This is the approach taken by black.

My main concern is with the init_exposed_model method, which initializes all fields of ModelRpcServer, but it does so outside of the conventional __init__ function. This results in a lot of Pylint warnings and complicates the process of tracking class members.

[Qubitium]

@hnyls2002 If project sticks with black, I will follow suite.

Can black be tweaked to be less, strict? The following expansion is pure badness. Python has is own guideline on max width but black takes to another, almost unnecessary level.

[merrymercy]

@hnyls2002 The PR looks good to me. Please resolve the conflicts and you can merge it by yourself.