[Tests] Add regression tests for use_kernels=True crash on Qwen3Next and Qwen3.5

[kpal002]

What this PR does

Adds test_kernelize_does_not_crash to Qwen3NextModelTest and Qwen3_5TextModelTest.

Root cause (from issue #46399)

Setting model.use_kernels = True on either model raises:

ValueError: Attempted to register a kernel for apply_rotary_pos_emb,
but it was not a torch.nn.Module.
This means the underlying function needs to be decorated with
@use_kernel_func_from_hub.

The generated modeling files for Qwen3Next and Qwen3.5 define a local
apply_rotary_pos_emb (partial-RoPE variant) without
@use_kernel_func_from_hub, but the attention class still inherits
@use_kernelized_func(apply_rotary_pos_emb) from the parent class via the
modular converter's decorator fallback. When kernelize() tries to register
the plain function as an nn.Module, it crashes.

This PR

• Adds two @require_kernels-gated tests, one per model.
• Tests currently fail (they reproduce the crash). They will pass once the
  modular converter fix lands in the follow-up PR.

Follow-up PRs (tracked in #46399)

• PR 2: Fix utils/modular_model_converter.py — strip @use_kernelized_func(fn) from generated classes when fn is defined locally without @use_kernel_func_from_hub.
• PR 3: Regenerate modeling_qwen3_next.py and modeling_qwen3_5.py using the fixed converter.
• Future: Wire @use_kernel_func_from_hub("rotary_pos_emb_partial") once kernels-community#919 ships.

Closes #46399 (partial — regression test step)

cc @MekkCyber @vasqu @ArthurZucker @drbh

Before submitting

• This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
• Did you read the contributor guideline?
• Did you discuss your PR/implementation with the related model author(s) in the issue?
• Did you update the documentation with the relevant changes?
• Did you write any new necessary tests?

[github-actions]

[For maintainers] Suggested jobs to run (before merge)

run-slow: qwen3_5, qwen3_next