[core][graphIO] Improve node type version handling

* Deserialization: Replace the logic that defaulted the node type version to "0.0" when unspecified,
and assume that unspecified version on a node is targetting current node type version.
* Serialization: Only serialize node type versions for which a version info is available.

* Test suites:
  * Add helper context manager to manually override the version of a given node type.
  * Add new unit tests to cover version conflicts handling is various scenarios.

tests/utils.py

@@ -1,7 +1,9 @@
 from contextlib import contextmanager
+from unittest.mock import patch
 from typing import Type
-from meshroom.core import registerNodeType, unregisterNodeType
 
+import meshroom
+from meshroom.core import registerNodeType, unregisterNodeType
 from meshroom.core import desc
 
 @contextmanager
@@ -13,3 +15,14 @@ def registeredNodeTypes(nodeTypes: list[Type[desc.Node]]):
 
     for nodeType in nodeTypes:
         unregisterNodeType(nodeType)
+
+@contextmanager
+def overrideNodeTypeVersion(nodeType: Type[desc.Node], version: str):
+    """Helper context manager to override the version of a given node type."""
+    unpatchedFunc = meshroom.core.nodeVersion
+    with patch.object(
+        meshroom.core,
+        "nodeVersion",
+        side_effect=lambda type: version if type is nodeType else unpatchedFunc(type),
+    ):
+        yield