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_

Start in src/diffusers/models/attention_dispatch.py and inspect how the flash-attention functions are resolved from kernels-community/flash-attn2. Compare the requested _wrapped_* attributes with the exposed function names in the issue, then verify that the dispatcher proceeds through the flash-attention path using the current kernel package.

Written by the indexing model from the issue text.