ipywidgets performance can be slow whe used over a network

[sdissegna-maystreet]

This is very noticeable in projects such as https://github.com/cdr/code-server. The synchronization forces ipywidgets to wait for a browser-server round trip before sending the next message.

Environment data

• VS Code version: https://github.com/cdr/code-server latest (it's likely to happen in other environments such as gitpod or codespaces)
• Jupyter Extension version (available under the Extensions sidebar): master
• Python Extension version (available under the Extensions sidebar): v2021.10.1336267007
• OS (Windows | Mac | Linux distro) and version: macOS 10.15
• Python and/or Anaconda version: 3.9
• Type of virtual environment used (N/A | venv | virtualenv | conda | ...): venv
• Jupyter server running: Local

Expected behaviour

Performance is acceptable over a network.

Actual behaviour

10-20 widgets are enough to make a cell take many seconds to render the widgets

Steps to reproduce:

import ipywidgets as w
children = [w.Button() for _ in range(0, 100)]
w.HBox(children=children)

[rchiodo]

/verified