fix: correct type annotations and broken get_model_client imports

[kohankhaki]

PR Type

Fix

Short Description

Fix mypy type errors in generator, moderator, and scientist files:

• Replace broken get_model_client imports with get_standard_model_client (function was renamed but 4 files weren't updated)
• Make langfuse_client a required parameter instead of Optional[Langfuse] = None (the code already requires it - would crash at runtime if None)
• Fix untyped dict parameters to Dict[str, Any]

Tests Added

N/A