Dtype mismatch with LitGPT and autocast

Nobody has claimed this yet.

## 🐛 Bug

### To Reproduce

```python
import thunder
from thunder.tests.litgpt_model import GPT
import torch

device = torch.device("cuda")
with device:
model = GPT.from_name("llama2-like")
x = torch.randint(0, 100, (2, 5))
model = thunder.jit(model)

with torch.autocast("cuda", torch.float16):
model(x)

print("Good!")
```

I believe the problem is in this `cat`

https://github.com/Lightning-AI/lightning-thunder/blob/main/thunder/tests/lit_gpt_model.py#L484

Where `q_roped` is in `float32` and the non-roped bits in `float16`

cc @crcrpar

Start with thunder/tests/lit_gpt_model.py around line 484, where the reported torch.cat combines q_roped with the non-roped values. Run the provided LitGPT reproduction under torch.autocast("cuda", torch.float16) and inspect the operand dtypes and resulting failure. Done means the reproduction completes and the relevant behavior is covered by a regression test.

Written by the indexing model from the issue text.