Add Python type hint for tests and demos.

[trivialfis]

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[Copilot]

Pull Request Overview

This pull request adds comprehensive type annotations to test files and demo scripts across the XGBoost codebase. The changes improve code maintainability by making function signatures explicit with return types and parameter types.

Key Changes

• Added -> None return type annotations to test functions across GPU, Dask, and demo test suites
• Added type annotations for function parameters (e.g., str, int, bool, Dict, np.ndarray)
• Updated type hints in sklearn.py to add default value for optional parameter
• Removed unused imports (os, sys, matplotlib)
• Consolidated lint paths in ops/script/lint_python.py to use directory-level entries
• Updated comments and documentation strings

Reviewed Changes

Copilot reviewed 24 out of 24 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
tests/test_distributed/test_with_dask/test_with_dask.py	Added return type -> None and parameter type annotations to test functions, updated type hints for dask collection types
tests/test_distributed/test_with_dask/test_demos.py	Added -> None return type to all test functions
tests/python-gpu/test_*.py	Added comprehensive type annotations to test methods and functions across multiple GPU test files
tests/python-gpu/conftest.py	Added type annotations to pytest fixtures and hooks
python-package/xgboost/sklearn.py	Added default value = None to optional sample_weight parameter in protocol definition
ops/script/lint_python.py	Consolidated individual file entries into directory-level paths for linting
demo/guide-python/*.py	Added type annotations to demo functions and variables

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