Vulkan Q8 Conv2D: specialize shader on static parameters and tensor s…

[SS-JIA]

…izes

This change moves all fixed Conv2D parameters (kernel shape, stride, padding, dilation, groups) and the input/output tensor dimensions into Vulkan specialization constants. By making these values compile-time constants, the backend can generate more optimized pipelines, eliminate generic fallback paths, and reduce dynamic indexing overhead. This significantly improves performance across large and compute-intensive convolution workloads.

Change-Id: I3efe3de80dece91341ae4111bef1254c6779a1db

Summary

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[PLEASE REMOVE] If this PR closes an issue, please add a Fixes #<issue-id> line.

[PLEASE REMOVE] If this PR introduces a fix or feature that should be the upcoming release notes, please add a "Release notes: " label. For a list of available release notes labels, check out CONTRIBUTING.md's Pull Requests.

Test plan

[PLEASE REMOVE] How did you test this PR? Please write down any manual commands you used and note down tests that you have written if applicable.

cc @manuelcandales @digantdesai @cbilgin

[pytorch-bot]

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❌ 1 New Failure, 1 Unrelated Failure

As of commit 93b38be with merge base 42e3222 ():

NEW FAILURE - The following job has failed:

• Lint / lintrunner / linux-job (gh)
  >>> Lint for backends/vulkan/test/custom_ops/utils.cpp:

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

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

• pull / android / run-emulator (gh) (trunk failure)
  Timeout waiting for emulator to boot.

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