Introduce Chars

This improves the implementation by introducing a class to manage the characters

src/ilp_keyboard_layout_optimization/data_aquisition/chars.py

@@ -2,9 +2,11 @@
 
 __all__ = ["Chars"]
 
-from typing import Optional, Union
+import string
+from itertools import product
+from typing import Optional, Tuple, Union
 
-from src.ilp_keyboard_layout_optimization.type_aliases import CharTuple
+from ..type_aliases import Bigram, CharTuple
 
 
 class Chars: