[WIP] Fix performance issues when pasting nodes

[Claude]

Thanks for asking me to work on this. I will get started on it and keep this PR's description up to date as I form a plan and make progress.

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This section details on the original issue you should resolve

<issue_title>[bug] Performance issues when pasting nodes</issue_title>
<issue_description>Describe the bug

When we paste nodes the whole graph is cleared and re-created, which can bring performance issues

To Reproduce

• Copy a node (Ctrl+C)
• Add a breakpoint on this line :
  

  Meshroom/meshroom/ui/commands.py

  Line 230 in 0ab90c0

  graph._deserialize(self.data)

• Paste it (Ctrl+V)
• Explore the call stack :

  • Meshroom/meshroom/ui/graph.py

    Line 1616 in 0ab90c0

    result = self.push(commands.PasteNodesCommand(self._graph, graphData, pos))

  • Meshroom/meshroom/ui/commands.py

    Line 230 in 0ab90c0

    graph._deserialize(self.data)

  • Meshroom/meshroom/core/graph.py

    Line 307 in 0ab90c0

    self._clearGraphContent()

    -> the graph is cleared before being re-created</issue_description>

Comments on the Issue (you are @claude[agent] in this section)