Doc: references for `lfilter` implementation

[yoyololicon]

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[bot]]

:link: Helpful Links

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

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:white_check_mark: You can merge normally! (2 Unrelated Failures)

As of commit 7be5a28304216915d20f5e2a50b058685d0dfcee with merge base b2d9c3e315405f2b5cfdfa5b93f849d5b27a4109 ():

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

* [Unittests on Windows CPU / unittests-windows-cpu / windows-job](https://hud.pytorch.org/pr/pytorch/audio/3734#20876911441) ([gh](https://github.com/pytorch/audio/actions/runs/7660179913/job/20876911441)) `ImportError: DLL load failed while importing _C: The specified module could not be found.` * [Unittests on Windows GPU / unittests-windows-gpu / windows-job](https://hud.pytorch.org/pr/pytorch/audio/3734#20876911434) ([gh](https://github.com/pytorch/audio/actions/runs/7660179912/job/20876911434)) `ImportError: DLL load failed while importing _C: The specified module could not be found.`

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[mthrok]

Feel free to merge!