Upgrade to jupyterlab 4

[peytondmurray]

This PR updates this extension to jupyterlab 4. Given that this relies on registering an ipython magic, and given that there's not much to the frontend, there wasn't much to change here.

With jupyterlab==4.0.0rc1 everything seemed to work just fine when I loaded the extension (%load_ext jupyterlab_notify) and then ran

%%notify
import time
time.sleep(1)

@mlucool I bumped the patch version - are you okay with this or should I bump the minor (or major) version instead?

[mlucool]

This would be a major version as if you upgraded and were on lab@3.x I think it would break

[singharpit94]

Tested that with jupyterlab4, things are working as expected, post test passing and version bump, we can merge.

[peytondmurray]

@singharpit94 Looks good now!