Add pyoxigraph stub for NamedNode

python/pyoxigraph.pyi

@@ -0,0 +1,15 @@
+from typing import Any
+
+class NamedNode:
+    @property
+    def value(self) -> str: ...
+    def __init__(self, value: str) -> None: ...
+    def __str__(self) -> str: ...
+    def __repr__(self) -> str: ...
+    def __hash__(self) -> int: ...
+    def __eq__(self, other: Any) -> bool: ...
+    def __ge__(self, other: Any) -> bool: ...
+    def __gt__(self, other: Any) -> bool: ...
+    def __le__(self, other: Any) -> bool: ...
+    def __lt__(self, other: Any) -> bool: ...
+    def __ne__(self, other: Any) -> bool: ...