fix(graph-workflow): pass a dict to Edge.from_nodes' metadata argument

Edge normalizes with 'metadata or {}', so kwargs and 'kwargs if kwargs
else None' produce the identical edge; the Optional form only made Pyre
report an incompatible parameter type at the call site.

Author: ayaangazali

swarms/structs/graph_workflow.py

@@ -828,7 +828,7 @@ def from_nodes(
 
         # Put all kwargs into metadata dict
         condition = kwargs.pop("condition", None)
-        metadata = kwargs if kwargs else None
+        metadata = kwargs
         return cls(
             source=src,
             target=tgt,