attention dispatcher assumes wrong attributes for flash attn kernel from hub

### Describe the bug

The breakage was in the active diffusers checkout, not in kernels. kernels-community/flash-attn2 exposes:

- `flash_attn_varlen_func`
- `flash_attn_varlen_qkvpacked_func`
- `flash_attn_interface._flash_attn_varlen_forward`
- `flash_attn_interface._flash_attn_varlen_backward`

But diffusers was trying to resolve:

- `flash_attn_interface._wrapped_flash_attn_varlen_forward`
- `flash_attn_interface._wrapped_flash_attn_varlen_backward`

Those _wrapped_* attrs do not exist in the current kernels package. I patched `src/diffusers/models/attention_dispatch.py` to use the actual `_flash_attn_varlen_forward`/`...backward` names, which allowed it to proceed.

### Reproduction

No separate MRE

### Logs

```shell

```

### System Info

Not needed

### Who can help?

_No response_

Inizia in src/diffusers/models/attention_dispatch.py e ispeziona come vengono risolte le funzioni di flash-attention da kernels-community/flash-attn2. Confronta gli attributi _wrapped_* richiesti con i nomi delle funzioni esposti nell’issue, quindi verifica che il dispatcher proceda attraverso il percorso flash-attention usando il pacchetto kernel corrente.

Scritto dal modello di indicizzazione a partire dal testo della issue.