Move prop.py as __init__.py into a directory

pyproject.toml

@@ -184,7 +184,7 @@ extend-safe-fixes = [
     "N999",   # module name
     "PT027",  # assertRaises
 ]
-"src/icalendar/prop.py" = [
+"src/icalendar/prop/__init__.py" = [
     "N801",   # Class name should use CamelCase
 ]
 "src/icalendar/fuzzing/*" = [

src/icalendar/prop/__init__.py

@@ -717,6 +717,17 @@ class vDDDTypes(TimeBase):
             return vTime.from_ical(ical)
         raise ValueError(f"Expected datetime, date, or time. Got: '{ical}'")
 
+    @property
+    def td(self) -> timedelta:
+        """Compatibility property returning self.dt.
+
+        This class is used to replace different time components.
+        Some of them contain a datetime or date (.dt).
+        Some of them contain a timedelta (.td).
+        This property allows interoperability.
+        """
+        return self.dt
+
 
 class vDate(TimeBase):
     """Date