Add _node_value helper for safe node reads

Introduce a static _node_value(node_map, name, default) helper that performs a best-effort read of GenICam node values. It looks up the node, returns default if missing, then tries node.value and falls back to node.GetValue() while swallowing exceptions. This prevents debug helpers and open() from failing when test/SDK nodes expose different accessors or raise errors.

Author: C-Achard

dlclivegui/cameras/backends/gentl_backend.py

@@ -1093,6 +1093,32 @@ def _node(node_map, name: str):
         except Exception:
             return None
 
+    @staticmethod
+    def _node_value(node_map, name: str, default=None):
+        """Best-effort read of a GenICam node value.
+
+        Debug helpers must not make open() fail just because a value cannot be read.
+        Harvesters-style fake/test nodes usually expose `.value`; some SDK-style
+        nodes may expose `GetValue()`.
+        """
+        node = GenTLCameraBackend._node(node_map, name)
+        if node is None:
+            return default
+
+        try:
+            return node.value
+        except Exception:
+            pass
+
+        try:
+            getter = getattr(node, "GetValue", None)
+            if getter is not None:
+                return getter()
+        except Exception:
+            pass
+
+        return default
+
     @staticmethod
     def _node_symbolics(node) -> list[str]:
         try: