Add dvars black

[Nauman702]

updated for style (after installing black)

[Nauman702]

@oesteban Please check. I installed the black and updated metrics.py file. Thanks

[oesteban]

You have a conflict in scripts/validate_data.py.

The reason for this conflict to appear is that this commit (probably mistakenly) adds one more file (scripts/validate_data.py) to the changes.

There are two relevant aspects to note here:

• Adding changes extraneous to the core objective of a pull request is almost always problematic. In this case, disallows a direct/clean merge of the code (you'll see the merge button disabled).
• But perhaps more importantly, this has brought to my attention that the file scripts/validate_data.py was not up-to-date in your main branch of the repository.

Let's fix that problem first.

1. Let's start a new branch from this one:

   git checkout -b rescue-validate-data-edits main

2. Let's now bring the changes to scripts/validate_data.py from the new branch:

   git checkout add-dvars-black -- scripts/validate_data.py

3. Let's run black on the file and make sure it is more readable:

   black scripts/validate_data.py

4. Add, commit, and push:

   git add scripts/validate_data.py
   git commit -m "enh: add implementation of data validation (exercise response)"
   git push -u origin rescue-validate-data-edits

5. Request a PR and merge it after the feedback.

Once we make sure your code in scripts/validate_data.py is not going to waste, we will come back to this PR and finally resolve the conflict.