refactor(utils): add static type annotations and fix validation logic in _validation.py

[mani787060]

Description

This PR improves code quality, type safety, and internal logic consistency within imblearn/utils/_validation.py.

Summary of Changes

• Added complete static type annotations across _validation.py.
• Fixed typo in check_target_type exception string (multiclasss -> multiclass).
• Corrected parameter mismatch in check_target_type docstring (indicate_one_vs_all).
• Activated _is_neighbors_object validation inside check_neighbors_object.
• Fixed internal method typos in ArraysTransformer (_transfrom_one -> _transform_one, _gets_props -> _get_props).
• Reorganized module constants to the top level.

Checklist

• Code adheres to the project's style guidelines.
• Relevant functions have clear docstrings and typing annotations.