fix: use valid string types for sampler/scheduler in _ALL_PINS

Fix FlakeDataSplitSelect not creatable: _ALL_PINS used _SAMPLER_TYPES[0] and [1]
which are tuples/lists when comfy.samplers imports successfully, not valid
RETURN_TYPES strings. Use plain 'SAMPLER'/'SCHEDULER' type names instead.

flake_data_nodes.py

@@ -24,8 +24,8 @@ _ALL_PINS = [
     ("height", "INT"),
     ("steps", "INT"),
     ("cfg", "FLOAT"),
-    ("sampler_name", _SAMPLER_TYPES[0]),
-    ("scheduler", _SAMPLER_TYPES[1]),
+    ("sampler_name", "SAMPLER"),
+    ("scheduler", "SCHEDULER"),
 ]