[BUG] Name error during importing when camel is not installed

[dandansamax]

What version of camel are you using?

0.1.2

System information

pass

Problem description

When camel extra is not installed, the type annotation in camel_model.py will cause Name Error.
https://github.com/camel-ai/crab/blob/48b6f4e66c8451f39cd7da5eeb785c5f9f935bd7/crab/agents/backend_models/camel_model.py

Reproducible example code

The Python snippets:

Command lines:

Extra dependencies:

Steps to reproduce:

Traceback

Traceback (most recent call last):
  File "/home/dandan/.pyenv/versions/3.10.12/lib/python3.10/runpy.py", line 196, in _run_module_as_main
    return _run_code(code, main_globals, None,
  File "/home/dandan/.pyenv/versions/3.10.12/lib/python3.10/runpy.py", line 86, in _run_code
    exec(code, run_globals)
  File "/home/dandan/Programs/crab-publish/crab-benchmark-v0/main.py", line 27, in <module>
    from crab.agents.backend_models import ClaudeModel, GeminiModel, OpenAIModel
  File "/home/dandan/Programs/crab-publish/crab/agents/backend_models/__init__.py", line 15, in <module>
    from .camel_model import CamelModel
  File "/home/dandan/Programs/crab-publish/crab/agents/backend_models/camel_model.py", line 37, in <module>
    def find_model_platform_type(model_platform_name: str) -> ModelPlatformType:
NameError: name 'ModelPlatformType' is not defined

Expected behavior

No response

Additional context

No response