remove warning from nbdev as pkg_resources is already deprecated

[kurianbenoy-sarvam]

@jph00 I have constantly getting this warning in my nbdev projects for the last few months. Today is the day to fix it.

The pkg_resources package is slated for removal as early as 2025-11-30. Refrain from using this package or pin to Setuptools<81.
import pkg_resources,importlib

(sarvamai-dubbing) ➜  sarvamai-dubbing git:(main) ✗ nbdev_prepare
/Users/kurianbenoy/git/dubbing-repos/sarvamai-dubbing/.venv/lib/python3.12/site-packages/nbdev/doclinks.py:20: UserWarning: pkg_resources is deprecated as an API. See https://setuptools.pypa.io/en/latest/pkg_resources.html. The pkg_resources package is slated for removal as early as 2025-11-30. Refrain from using this package or pin to Setuptools<81.
  import pkg_resources,importlib

• Many thanks to you and @hamelsmu for building nbdev. I now maintain packages with 1M+ downloads all thanks to you. I hope you remeber me, as I was the kid, who got kicked off from fast.ai class :)