Add support for Qwen3.5 MoE

[michaelroyzen]

Add Qwen3.5 MoE support to Liger Kernel

Summary

• Adds Liger Kernel optimizations for the Qwen3.5 MoE model family (qwen3_5_moe / qwen3_5_moe_text), targeting Transformers v5+
• Qwen3.5 MoE combines Qwen3 Next's hybrid GDN/attention architecture with Sparse MoE (shared + routed experts), so the implementation mirrors Qwen3 Next's Liger integration: Gemma-style RMSNorm (LigerRMSNormForQwen3Next), fused SwiGLU experts (LigerExperts), and fused linear cross-entropy loss

Changes

New file:

• src/liger_kernel/transformers/model/qwen3_5_moe.py — lce_forward for Qwen3_5MoeForCausalLM, based on the Qwen3 Next version with the load_balancing_loss_func import updated to point to Qwen3.5 MoE's local definition

Modified files:

• src/liger_kernel/transformers/monkey_patch.py — apply_liger_kernel_to_qwen3_5_moe function (RMSNorm, SwiGLU experts, fused LCE; RoPE disabled) with instance patching for norm layers, shared expert, and routed experts; registered as qwen3_5_moe and qwen3_5_moe_text in MODEL_TYPE_TO_APPLY_LIGER_FN
• src/liger_kernel/transformers/__init__.py — Export apply_liger_kernel_to_qwen3_5_moe in TYPE_CHECKING, __getattr__, and __all__
• test/utils.py — revert_liger_kernel_to_qwen3_5_moe for test cleanup
• test/convergence/fp32/test_mini_models.py — Availability check, imports, and MiniModelConfig entry for mini_qwen3_5_moe
• test/transformers/test_monkey_patch.py — is_qwen3_5_moe_available helper and test_apply_liger_kernel_to_instance_for_qwen3_5_moe verifying all patches are applied correctly

Test plan

• test_apply_liger_kernel_to_instance_for_qwen3_5_moe passes (monkey patch instance patching)
• mini_qwen3_5_moe convergence test passes (fp32 mini model)
• Existing Qwen3 Next and Qwen3 MoE tests still pass (no regressions)

[michaelroyzen]

@shimizust @Tcc0403

[michaelroyzen]

Convergence test passes

[Tcc0403]

@Mecoli1219 can you take a look?

[michaelroyzen]

Confirming Qwen3-Next still passes

[michaelroyzen]

Are we ready to merge @Tcc0403 @Mecoli1219?