Add spectrum codec

[LTMeyer]

This PR implements the codec for desi spectrum (stored at /mnt/ceph/users/polymathic/MMOMA/outputs/mmoma_codec_sdss+desi/6kzi0iz9/checkpoints/last.pt).

I checked I could reproduce the same encoded data as the original codec from the same random input.

Reflecting on this PR related to the other, we may want to reorganize a bit the codec. For instance, removing the pytorch-lightning dependencies make the codecs standard classes, whereas we would like them to be torch.nn.Module and ultimately offer HF support.

[Copilot]

Pull Request Overview

This PR implements a new autoencoder‐based codec for processing desi spectra in the Aion framework. Key changes include introducing a Spectrum modality with dedicated fields, implementing the SpectrumCodec along with its encoding/decoding logic using ConvNeXt-based modules and quantizers, and adding supporting test data and dependency updates.

Reviewed Changes

Copilot reviewed 12 out of 12 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
tests/tokenizers/test_spectrum_tokenizer.py	Added tests for the new spectrum codec using a Hugging Face–pretrained model.
tests/test_data/SPECTRUM_input_batch.pt	Added sample input data for spectrum modality.
tests/test_data/SPECTRUM_encoded_batch.pt	Added sample encoded output data for spectrum codec verification.
tests/test_data/SPECTRUM_decoded_batch.pt	Added sample decoded output data for spectrum codec verification.
pyproject.toml	Updated dependencies to include vector_quantize_pytorch.
aion/modalities.py	Introduced the Spectrum modality with fields for flux, ivar, mask, and wavelength.
aion/codecs/tokenizers/spectrum.py	Implemented a Spectrum codec class with autoencoder logic and quantization integration.
aion/codecs/quantizers/init.py	Added new LFQ and scalar quantizers for handling the latent space in the codec.
aion/codecs/modules/utils.py	Added custom LayerNorm and GRN utility modules.
aion/codecs/modules/spectrum.py	Provided interpolation functions and a latent spectral grid for converting between grids.
aion/codecs/modules/convnext.py	Added 1D ConvNeXt-based encoder and decoder modules for processing spectral data.