Support Hexadecimal Page Numbers (e.g. 1FF, 12E)

- Refactored  to parse page numbers as nibbles ((T<<4)|U) instead of decimal, preventing collisions between hex and decimal pages.
- Updated  to format page IDs as Hex.
- Updated  to display page IDs as Hex in the list.
- Ensures filler/housekeeping pages are correctly isolated.

src/teletext/models.py

@@ -81,7 +81,8 @@ class Page:
     
     @property
     def full_page_number(self):
-        return f"{self.magazine}{self.page_number:02d}"
+        # Format as Hex to support A-F pages
+        return f"{self.magazine}{self.page_number:02X}"
 
 @dataclass
 class TeletextService: