Update PygameUIKit to support latest Python version (3.12) with modern type hints

[Copilot]

This PR modernizes PygameUIKit to support the latest Python version (3.12) and adopts modern Python type hint syntax available in Python 3.10+.

Changes Made

Python Version Support

• Updated minimum Python requirement from >=3.7 to >=3.10
• Added explicit Python version classifiers for 3.10, 3.11, and 3.12 in pyproject.toml
• Updated GitHub Actions workflow to use Python 3.12 and latest action versions (v4)

Type Hint Modernization

The codebase has been updated to use modern Python type hint syntax:

Before:

from typing import Union
def best_contrast_color(rgb_color: Union[Color, tuple]):
    ...

def __init__(self, values: list[int], labels: list[str] = None):
    ...

self.actions: dict[int, callable] = {}

After:

def best_contrast_color(rgb_color: Color | tuple):
    ...

def __init__(self, values: list[int], labels: list[str] | None = None):
    ...

from collections.abc import Callable
self.actions: dict[int, Callable] = {}

Specific Updates

• Replaced typing.Union[Type1, Type2] with built-in Type1 | Type2 syntax
• Updated optional parameters to use Type | None instead of Type = None
• Replaced deprecated callable with collections.abc.Callable
• Removed unnecessary typing imports where built-in alternatives are available
• Fixed demo import paths for better package structure

Compatibility

• All existing functionality is preserved
• Backward compatibility maintained for Python 3.10+
• Modern type hints provide better IDE support and type checking
• All modules tested and verified to work correctly with Python 3.12.3

This update ensures PygameUIKit is ready for the latest Python ecosystem while maintaining clean, modern code that follows current Python best practices.

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