🔴 Fix EnCodec internals and integration tests (#39431)
* EnCodec fixes and update integration tests.
* Apply padding mask when normalize is False.
* Update comment of copied function.
* Fix padding mask within modeling.
* Revert padding function.
* Simplify handling of padding_mask.
* Address variable codebook size.
* Add output for padding for consistency with original model, fix docstrings.
* last_frame_pad_length as int
* Update example code.
* Improve docstring/comments.
* Shorten expected output.
* Consistent docstring.
* Parameterize tests.
* Properties for derived variables.
* Update expected outputs from GitHub runner.
* Consistent outputs with runner GPUs.
