Fix path_from_uri

[renkun-ken]

Looks like the vscode-notebook-cell uris look like the following on different platforms:

# Windows: vscode-notebook-cell:/c:/Users/Username/Documents/Notebooks/MyNotebook.ipynb#MyCellId
# Unix: vscode-notebook-cell:/home/username/Documents/Notebooks/MyNotebook.ipynb#MyCellId
# WSL: vscode-notebook-cell://wsl+ubuntu-20.04/home/username/Documents/Notebooks/MyNotebook.ipynb#MyCellId