Cleanup: add complete type hints across the codebase

[dbqpdb]

A handful of methods (e.g. Board.isValidFENboard, Board.is_FEN, Lexicon.spew) have type hints; most do not. Adding full hints will:

• improve IDE support and refactoring safety,
• enable mypy in CI later,
• document expected types for collaborators (especially around square_name, which currently accepts strings, lists, and tuples).

Suggested order: start with Board and Move (most callers depend on them), then Piece and its subclasses, then Game / GameController.

Related to #1.