Add conditional checks to _check_and_adjust_attn_implementation()

[zheliuyu]

What does this PR do?

To prevent unnecessary downloads by kernels, avoid installing kernels-community/flash-attn and kernels-community/vllm-flash-attn3 when attn_implementation=flash_attention_2 is specified for NPU.

test

script

from transformers import AutoModelForCausalLM, AutoTokenizer

model = AutoModelForCausalLM.from_pretrained(
    "Qwen/Qwen3-0.6B",
    device_map="auto",
    torch_dtype="auto",
    attn_implementation="flash_attention_2",
).eval()
print("Operation successful")

Before

`torch_dtype` is deprecated! Use `dtype` instead!
Fetching 0 files: 0it [00:00, ?it/s]
Traceback (most recent call last):
  File "/root/kernels-main/src/kernels/utils.py", line 144, in install_kernel
    return _load_kernel_from_path(repo_path, package_name, variant_locks)
  File "/root/kernels-main/src/kernels/utils.py", line 177, in _load_kernel_from_path
    raise FileNotFoundError(
FileNotFoundError: Kernel at path `/root/.cache/huggingface/hub/models--kernels-community--flash-attn/snapshots/90b3e941627659b28ff001c08b218315e1b7183b` does not have build: torch27-cxx11-cann81-aarch64-linux

After

`torch_dtype` is deprecated! Use `dtype` instead!
Operation successful

[zheliuyu]

@ArthurZucker @MekkCyber This PR is now ready for review.

[MekkCyber]

Indeed ! thanks for fixing

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