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

## 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"

Start by reading roll/utils/functionals.py and the type-hint requirement in CLAUDE.md. Begin with Phase 1's simple functions, then review partially annotated and custom-type functions as described; the work is done when the utility functions in that file have complete type annotations.

Written by the indexing model from the issue text.