refact: move Node, Edge and EdgeOnSet to models

tests/graphs/test_graph.py

@@ -1,6 +1,7 @@
 import pytest
 
-from plesna.graph.graph import Edge, Graph, Node
+from plesna.graph.graph import Graph
+from plesna.models.graphs import Edge, Node
 
 
 def test_append_nodess():
@@ -94,9 +95,7 @@ def test_get_sources_from(nodes, dag_edges):
     assert graph.get_direct_sources_from(nodes["C"]) == set([nodes["A"], nodes["B"]])
     assert graph.get_direct_sources_from(nodes["D"]) == set([nodes["C"]])
 
-    assert graph.get_sources_from(nodes["D"]) == set(
-        [nodes["A"], nodes["B"], nodes["C"]]
-    )
+    assert graph.get_sources_from(nodes["D"]) == set([nodes["A"], nodes["B"], nodes["C"]])
 
 
 def test_valid_dage(dag_edges, notdag_edges):

tests/graphs/test_graph_set.py

@@ -1,4 +1,5 @@
-from plesna.graph.graph_set import EdgeOnSet, GraphSet, Node
+from plesna.graph.graph_set import GraphSet
+from plesna.models.graphs import EdgeOnSet, Node
 
 
 def test_init():