Squashed commit of the following:

commit d7948acb
Author: Fabien Maniere <fabien.maniere@cnrs.fr>
Date:   Wed Jan 15 17:36:49 2025 +0100

    export to GEXF: adding the weight attribute to all nodes

commit d937e72e
Author: Fabien Manière <fmaniere.pro@gmail.com>
Date:   Wed Apr 24 17:09:27 2024 +0200

    adding weight attribute

src/Gargantext/Core/Viz/Graph/GEXF.hs

@@ -51,19 +51,30 @@ graphToXML (G.Graph { .. }) = root _graph_nodes _graph_edges
         desc = XML.tag "description" mempty $ XML.content "Gargantext gexf file"
 
     graph :: (Monad m) => [G.Node] -> [G.Edge] -> ConduitT i XML.Event m ()
-    graph gn ge = XML.tag "graph" params $ (nodes gn) <> (edges ge)
+    graph gn ge = XML.tag "graph" params $ graphAttributes <> (nodes gn) <> (edges ge)
       where
         params = XML.attr "mode" "static"
               <> XML.attr "defaultedgetype" "directed"
 
+    graphAttributes :: (Monad m) => ConduitT i XML.Event m ()
+    graphAttributes = XML.tag "attributes" graphAttributesParams $ graphAttributeWeight
+      where
+        graphAttributesParams = XML.attr "class" "node"
+        graphAttributeWeight = XML.tag "attribute" attrWeightParams $ XML.content ""
+        attrWeightParams = XML.attr "id" "0"
+                        <> XML.attr "title" "weight"
+                        <> XML.attr "type" "integer"
+
     nodes :: (Monad m) => [G.Node] -> ConduitT i XML.Event m ()
     nodes gn = XML.tag "nodes" mempty (yieldMany gn .| awaitForever node')
     node' :: (Monad m) => G.Node -> ConduitT i XML.Event m ()
-    node' (G.Node { .. }) = XML.tag "node" params (XML.tag "viz:size" sizeParams $ XML.content "")
+    -- node' (G.Node { .. }) = XML.tag "node" params (XML.tag "viz:size" sizeParams $ XML.content "")
+    node' (G.Node { .. }) = XML.tag "node" params $ XML.tag "attvalues" mempty $ XML.tag "attvalue" sizeParams mempty
       where
         params = XML.attr "id" node_id
               <> XML.attr "label" node_label
-        sizeParams = XML.attr "value" (show node_size)
+        sizeParams = XML.attr "for" "0"
+                  <> XML.attr "value" (show node_size)
 
     edges :: (Monad m) => [G.Edge] -> ConduitT i XML.Event m ()
     edges ge = XML.tag "edges" mempty (yieldMany ge .| awaitForever edge')