[Type Hints] Add type annotations to utility functions in roll/utils/functionals.py

[guozhihao-224]

Description

The roll/utils/functionals.py file contains many utility functions missing type annotations. This tracks the effort to add complete type hints.

Current State

• ~30+ functions missing complete type annotations
• Some docstrings in Chinese

Proposed Phases

1. Phase 1: Simple functions (no existing type hints)
2. Phase 2: Add return types to partially annotated functions
3. Phase 3: Complex functions with custom types

Benefits

• Better IDE support and autocomplete
• Improved documentation
• Easier maintenance with type checking
• Consistency with CLAUDE.md standards

Related

Aligns with CLAUDE.md: "Type hints required for all code"