chore: add multipart dep for fastapi

[zhyncs]

Motivation

fix

root@hostname:/# python -m sglang.launch_server --model-path  casperhansen/llama-3-8b-instruct-awq  --disable-radix-cache
Form data requires "python-multipart" to be installed.
You can install "python-multipart" with:

pip install python-multipart

Traceback (most recent call last):
  File "/usr/lib/python3.10/runpy.py", line 196, in _run_module_as_main
    return _run_code(code, main_globals, None,
  File "/usr/lib/python3.10/runpy.py", line 86, in _run_code
    exec(code, run_globals)
  File "/usr/local/lib/python3.10/dist-packages/sglang/launch_server.py", line 5, in <module>
    from sglang.srt.server import launch_server
  File "/usr/local/lib/python3.10/dist-packages/sglang/srt/server.py", line 162, in <module>
    async def openai_v1_files(file: UploadFile = File(...), purpose: str = Form("batch")):
  File "/usr/local/lib/python3.10/dist-packages/fastapi/routing.py", line 944, in decorator
    self.add_api_route(
  File "/usr/local/lib/python3.10/dist-packages/fastapi/routing.py", line 883, in add_api_route
    route = route_class(
  File "/usr/local/lib/python3.10/dist-packages/fastapi/routing.py", line 519, in __init__
    self.body_field = get_body_field(dependant=self.dependant, name=self.unique_id)
  File "/usr/local/lib/python3.10/dist-packages/fastapi/dependencies/utils.py", line 817, in get_body_field
    check_file_field(final_field)
  File "/usr/local/lib/python3.10/dist-packages/fastapi/dependencies/utils.py", line 100, in check_file_field
    raise RuntimeError(multipart_not_installed_error) from None
RuntimeError: Form data requires "python-multipart" to be installed.
You can install "python-multipart" with:

pip install python-multipart

Modification

as titled

Checklist

1. Ensure pre-commit pre-commit run --all-files or other linting tools are used to fix potential lint issues.
2. Confirm that modifications are covered by complete unit tests. If not, please add more unit tests for correctness.
3. Modify documentation as needed, such as docstrings or example tutorials.