test and validate signup with dispersable keypad and login with non-dispersable keypad

src/customer_attributes.py

@@ -1,4 +1,4 @@
-from pydantic import BaseModel
+from pydantic import BaseModel, model_validator
 
 from src.models import KeypadSize
 from src.utils import generate_random_nonrepeating_list
@@ -9,6 +9,13 @@ class CustomerAttributes(BaseModel):
     set_vals: list[int]
     keypad_size: KeypadSize
 
+    @model_validator(mode='after')
+    def check_keys_vs_attrs(self):
+        if self.keypad_size.is_dispersable:
+            raise ValueError("number of keys must be less than the number of "
+                             "attributes per key to be dispersion resistant")
+        return self
+
     @staticmethod
     def new(keypad_size: KeypadSize):
         assert (keypad_size.numb_of_keys <= 256)