Merged three native APIs into one: get_server_info

[henryhmko]

Motivation

Merged Native API endpoints get_server_args, get_memory_pool_size, and get_max_num_tokens into one endpoint: get_server_info for cleaner code in server.py.

Modifications

Merged the three endpoints as mentioned above + Updated the docs/unittests accordingly.

Checklist

• Format your code according to the Contributor Guide.
• Add unit tests as outlined in the Contributor Guide.
• Update documentation as needed, including docstrings or example tutorials.

[ByronHsu]

Removing existing api routes can break existing users. Better to keep the old one and add get_server_info on top

[merrymercy]

I do not think they are ever used by any non-core developers, so we do not need to worry about the backward compatibility now.

[binarycrayon]

we actually use it, would love to get some warning about breaking changes in the future