Fix mypy strict mode and ruff lint errors

[Copilot]

CI was failing on tox -e lint and tox -e type due to missing type annotations and style violations.

Changes

Type annotations (mypy --strict compliance):

• Added return type annotations to all methods (-> None for __init__, specific types for others)
• Fixed implicit Optional by explicitly typing defaults: data: Optional[Dict[str, Any]] = None
• Added generic type parameters: Dict[str, Any], List[Any], Type[Any]
• Added cast() calls where _validate_base() returns lose type specificity
• Resolved name shadowing: used builtins.str in type hints within VBuilder class to disambiguate from the str() method

Linting (ruff compliance):

• Removed unused imports and variables
• Changed type comparisons from == to is for built-in types
• Split colon-separated statements onto separate lines
• Removed unused exception captures

Technical Note

The name shadowing issue was subtle - mypy correctly flagged that Dict[str, Any] within the VBuilder class scope could ambiguously refer to either the built-in str type or the VBuilder.str() method:

class VBuilder:
    def str(self) -> StringValidator:  # This shadows built-in str
        return StringValidator()
    
    # mypy sees 'str' here as potentially referring to the method above
    def list(self, item_validator: Union[Validator, Dict[str, Any], Type[Any]]) -> ListValidator:
        #                                                    ^^^

Using builtins.str explicitly resolves the ambiguity.

Original prompt

---

This section details on the original issue you should resolve

<issue_title>ci.ymlでmypyとlintのエラーの対処をしてください</issue_title>
<issue_description></issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes ci.ymlでmypyとlintのエラーの対処をしてください #2

---

✨ Let Copilot coding agent set things up for you — coding agent works faster and does higher quality work when set up for your repo.