implement net_listening

[gluneau]

remix.ethereum.org requires net_listening to operate in the Web3 Provider Environment mode

[1643223015194] DEBUG (3242770 on XPS-15-7590): incoming request
    jsonrpc: "2.0"
    id: 8517
    method: "net_listening"
    params: []
[1643223015196] DEBUG (3242770 on XPS-15-7590): request completed
    id: 8517
    jsonrpc: "2.0"
    error: {
      "code": -32601,
      "data": "The method net_listening does not exist / is not available.",
      "message": "Method not found"
    }

[gluneau]

This maybe required at the right spot for local development: res.setHeader('Access-Control-Allow-Private-Network', 'true');