Not able to run the Taskrunner or training code

Hi!
Great work! Congratulations! Thanks for releasing the code!

However, I am not able to reproduce the results for taskrunners using any of the `allenai/uio2-large`, `allenai/uio2-xl` or `allenai/uio2-xxl` models.
I am using `python 3.8` with `transformers 4.38.2`. Also downloaded the `tokenizer.model` from the official llama repo.

1. I tried using the code as:

```
import torch
from uio2.model import UnifiedIOModel
from uio2.preprocessing import UnifiedIOPreprocessor
from uio2.runner import TaskRunner
preprocessor = UnifiedIOPreprocessor.from_pretrained("allenai/uio2-preprocessor", tokenizer=tokenizer_path)
model = UnifiedIOModel.from_pretrained("allenai/uio2-large")
runner = TaskRunner(model, preprocessor)
image = runner.image_generation("a cat")
wavform = runner.audio_generation("dogs barking")
```

I am getting the error as
```
AttributeError: 'Decoder' object has no attribute 'generation_config'
```

Could you please let me know how to provide the `generation_config `?

2. Also, I tried the training code provided [here](https://github.com/allenai/unified-io-2.pytorch?tab=readme-ov-file#computing-the-loss) as

```
from torch.nn import functional as F
from uio2.preprocessing import build_batch
preprocessed_example = preprocessor(
text_inputs="What is 1+1?", text_targets="2", target_modality="text")
batch = build_batch([preprocessed_example], device=model.device)
out = model(batch)
total_loss = 0
for modality, (logits, targets, mask) in out.items():
losses = F.cross_entropy(
logits.view(-1, logits.shape[-1]), targets.view(-1).to(torch.long), reduction="none")
total_loss += (losses.reshape(logits.shape[:2])*mask)/mask.sum()
print(total_loss)
```

I am getting the `IndexError` while calculating `out = model(batch)` as:

```
/unified-io-2.pytorch/uio2/seq_features.py:160), in concat_sequences(seqs)
seq_lens = [x.seq_len for x in seqs]
out = {}
for k in dataclasses.fields(seqs[0]):
k = k.name
args = [expand_scalar(getattr(seq, k), seq.seq_len) for seq in seqs]
IndexError: list index out of range
```

3. When I tried to call [generation](https://github.com/allenai/unified-io-2.pytorch?tab=readme-ov-file#generation) as:

```
from uio2.preprocessing import build_batch
preprocessed_example = preprocessor(text_inputs="What color is the sky?", target_modality="text")
batch = build_batch([preprocessed_example], device=model.device)
tokens = model.generate(batch, modality="text", max_new_tokens=128)
```

I am getting the error (even though I provided modality as `text`) as:

```
unified-io-2.pytorch/uio2/model.py:551
if modality not in self.target_embedders:
ValueError(f"No target encoder for {modality}")
```