Improve type annotations throughout pystemd

[aleivag]

This commit modernizes and enhances type annotations across the codebase:

• Add comprehensive type annotations to pystemd.run function signature including all 30 parameters and return type
• Create SupportsFileno Protocol for proper typing of file-like objects
• Add from future import annotations to all Python source files for forward compatibility
• Migrate from old typing syntax to modern Python 3.10+ syntax:
  • Union[A, B] -> A | B
  • Optional[T] -> T | None
  • List[T] -> list[T]
  • Tuple[T, ...] -> tuple[T, ...]
  • Dict[K, V] -> dict[K, V]
• Update init.pyi stub file to match improved run() signature
• Add proper type annotations to exit method in base.py
• Remove unused typing imports (Union, Optional, List, Tuple, Dict) where replaced by modern syntax

These changes improve IDE support, enable better static type checking, and make the codebase more maintainable while maintaining backward compatibility with Python 3.10+.