refactor(graphgen): update imports and adapt GraphGen class

[Tendo33]

• Reorder and format import statements for better readability
• Update GraphGen class to use field() for default values of wiki_client and traverse_strategy to void

    raise ValueError(f'mutable default {type(f.default)} for field '
ValueError: mutable default <class 'graphgen.models.search.wiki_search.WikiSearch'> for field wiki_client is not allowed: use default_factory

    raise ValueError(f'mutable default {type(f.default)} for field '
ValueError: mutable default <class 'graphgen.models.strategy.travserse_strategy.TraverseStrategy'> for field traverse_strategy is not allowed: use default_factory

[Copilot]

Pull Request Overview

This PR refactors the GraphGen module by reorganizing import statements for improved readability and updating the GraphGen class to avoid using mutable defaults for its fields.

• Reformatted and grouped import statements
• Updated wiki_client and traverse_strategy to use field(default_factory=...) to prevent mutable default issues

[ChenZiHong-Gavin]

LGTM, thanks