carry sign and tradition through the Python bindings too

The bindings hand-map DayJson field by field, so the two fields added with
Greek and Slavic usage were in --json and not in to_dict(). The parity test
would have caught it; this is the fix rather than the discovery.

Both are getters as well, since every other field is.

python/typikon/_typikon.pyi

@@ -28,6 +28,12 @@ class Day:
     @property
     def rank(self) -> str | None: ...
     @property
+    def sign(self) -> str | None:
+        """The mark the liturgical books print beside a day of this rank."""
+    @property
+    def tradition(self) -> str:
+        """Greek or Slavic usage, as this jurisdiction reads the Typikon."""
+    @property
     def title(self) -> str:
         """The feast if there is one, else the principal commemoration."""
     @property