Doc: references for lfilter implementation

[yoyolicoris]

Add references to @yoyololicon and @forgi86's works for the core implementation of lfilter.
@forgi86 implemented the same logic as torchaudio's in forgi86/dynonet for efficient backpropagation.

[pytorch-bot]

🔗 Helpful Links

🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/audio/3734

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✅ You can merge normally! (2 Unrelated Failures)

As of commit 7be5a28 with merge base b2d9c3e ():

FLAKY - The following jobs failed but were likely due to flakiness present on trunk:

• Unittests on Windows CPU / unittests-windows-cpu / windows-job (gh)
  ImportError: DLL load failed while importing _C: The specified module could not be found.
• Unittests on Windows GPU / unittests-windows-gpu / windows-job (gh)
  ImportError: DLL load failed while importing _C: The specified module could not be found.

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[mthrok]

Thanks for the PR. Looks good but the linter is failing.

[mthrok]

LGTM

[mthrok]

Feel free to merge!