Add topk.py to BUCK

[kirklandsign]

Summary: Fix build

Differential Revision: D97649745

[pytorch-bot]

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❌ 1 Awaiting Approval, 1 New Failure, 2 Unrelated Failures

As of commit 444975d with merge base f7977a6 ():

AWAITING APPROVAL - The following workflow needs approval before CI can run:

• Claude Code (gh)

NEW FAILURE - The following job has failed:

• pull / unittest-editable / linux / linux-job (gh)
  backends/xnnpack/test/ops/test_conv2d.py::TestConv2d::test_qs8_conv2d_bn

BROKEN TRUNK - The following jobs failed but were present on the merge base:

👉 Rebase onto the `viable/strict` branch to avoid these failures

• pull / unittest / windows / windows-job (gh) (trunk failure)
  ##[error]The operation was canceled.
• pull / unittest-editable / windows / windows-job (gh) (trunk failure)
  ##[error]The operation was canceled.

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[meta-codesync]

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[Copilot]

Pull request overview

This PR fixes Buck build packaging for the CUDA Triton kernels by ensuring the newly added topk Triton kernel is included in the triton_kernels Python library target.

Changes:

• Add backends/cuda/triton/kernels/topk.py to the triton_kernels srcs list in backends/cuda/TARGETS.

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[Copilot]

triton/kernels/__init__.py unconditionally imports executorch.backends.cuda.triton.kernels.fused_moe, but triton/kernels/fused_moe.py is not listed in this triton_kernels target's srcs. This can break Buck packaging/imports (any import of ...triton.kernels.* executes __init__.py). Add triton/kernels/fused_moe.py to srcs (and consider adding other imported kernel modules as needed), or make the import conditional in __init__.py if it’s intentionally excluded from the target.

Suggested change

	"triton/kernels/topk.py",
	"triton/kernels/topk.py",
	"triton/kernels/fused_moe.py",