bump: torchaudio to 2.7.*

[deependujha]

Before submitting

• Was this discussed/agreed via a Github issue? (no need for typos and docs improvements)
• Did you read the contributor guideline, Pull Request section?
• Did you make sure to update the docs?
• Did you write any new necessary tests?

What does this PR do?

From Torchaudio >=2.9, Most APIs marked as pytorch/audio#3902 (comment) are now removed. This results in CI tests failing for litdata-torchaudio dataset optimization. check failing tests here.

We can either bump torchaudio to older release as a quick fix, or for latest torchaudio support, we need to update existing api calls, and install ffmpeg followed by torchcodec to pass tests.

As a quick fix, this PR pins torchaudio to an older compatible release to restore CI stability.

If we’d prefer to support the latest Torchaudio release instead, I can update this PR to include the necessary API adjustments and add ffmpeg, torchcodec, and torchaudio installation steps in the CI workflow.

PR review

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 80%. Comparing base (e69fdd0) to head (74879f9).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@         Coverage Diff         @@
##           main   #738   +/-   ##
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  Coverage    80%    80%           
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  Files        52     52           
  Lines      7330   7330           
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  Hits       5868   5868           
  Misses     1462   1462           

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