Add posibility to pack in _wikitext.py

[krammnic]

Context

What is the purpose of this PR? Is it to

• add a new feature
• fix a bug
• update tests and/or documentation
• other (please add here)

Please link to any issues this PR addresses.
Closes #1794

Changelog

What are the changes made in this PR?
#1794

Test plan

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• run pre-commit hooks and linters (make sure you've first installed via pre-commit install)
• add unit tests for any new functionality
• update docstrings for any new or updated methods or classes
• run unit tests via pytest tests
• run recipe tests via pytest tests -m integration_test
• manually run any new or modified recipes with sufficient proof of correctness
• include relevant commands and any other artifacts in this summary (pastes of loss curves, eval results, etc.)

UX

If your function changed a public API, please add a dummy example of what the user experience will look like when calling it.
Here is a docstring example
and a tutorial example

• I did not change any public API
• I have added an example to docs or docstrings

As my previous PR was merged, reopened this to fix merge conflict

[pytorch-bot]

🔗 Helpful Links

🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/torchtune/1807

• 📄 Preview Python docs built from this PR

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✅ No Failures

As of commit 2185935 with merge base c5b7386 ():
💚 Looks good so far! There are no failures yet. 💚

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[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 67.08%. Comparing base (54673b7) to head (2185935).
Report is 8 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1807      +/-   ##
==========================================
+ Coverage   67.05%   67.08%   +0.02%     
==========================================
  Files         305      305              
  Lines       15937    15948      +11     
==========================================
+ Hits        10687    10698      +11     
  Misses       5250     5250              

☔ View full report in Codecov by Sentry.
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[krammnic]

New example has already been in issue

[joecummings]

LGTM