model : add tokenizer from LFM2.5-Audio-1.5B (#19687)

model : add tokenizer from LFM2.5-Audio-1.5B (#19687)

* model : Add tokenizer from LFM2.5-Audio-1.5B

[LFM2.5-Audio-1.5B](https://huggingface.co/LiquidAI/LFM2.5-Audio-1.5B) introduced lightweight audio tokenizer.

Tokenizer based on LFM2 architecture and acts as "embedding" model with
different input `n_embd` and output `n_embd_out`.

To be used in https://github.com/ggml-org/llama.cpp/pull/18641.

To convert use

```shell
python3 convert_hf_to_gguf.py /path/to/LFM2.5-Audio-1.5B/audio_detokenizer
```

* Update convert_hf_to_gguf.py

Co-authored-by: Sigbjørn Skjæret <redacted>
* Formatting

* Rework check for attention layers

* Add LFM2 SWA model support

* Address PR feedback

* Set vocab to none

* Move helper function definitions to cpp file

---------

Co-authored-by: Sigbjørn Skjæret <redacted>