Remove dep on traitlet

Hi!
as we discovered, the dependency on traitlet >= 5 means that actually, the comm project requires python >= 3.7 contrary to what is published (claims to support python 3.6)

I've seen that the traitlet dependency is used just in order to import this : https://github.com/ipython/traitlets/blob/main/traitlets/utils/importstring.py , which is pretty stable and easy

I suggest to just copy the method in comm package and remove the dep on traitlet all-together
what do you think ?

Start by locating where the comm package imports traitlets.utils.importstring and compare it with traitlets' importstring.py implementation linked in the issue. Remove the dependency while preserving the package's stated Python 3.6 support, then run the existing test suite; the issue does not name specific files or tests.

Written by the indexing model from the issue text.