[ET-VK][custom_ops] Standardize binary filenames to test_*.cpp

[SS-JIA]

Stack from ghstack (oldest at bottom):

• -> [ET-VK][custom_ops] Standardize binary filenames to test_*.cpp #19571
• [ET-VK][custom_ops] Standardize test case label format across binaries #19570
• [ET-VK][custom_ops] Probe-then-scale adaptive dispatch stacking in test framework #19569

Five custom_ops test binaries did not follow the test_*.cpp naming convention used by the other 16. Rename them via sl mv (history-preserving) in both xplat and fbcode mirrors:

• add.cpp -> test_add.cpp
• choose_qparams_per_row.cpp -> test_choose_qparams_per_row.cpp
• q4gsw_linear.cpp -> test_q4gsw_linear.cpp
• q8csw_conv2d.cpp -> test_q8csw_conv2d.cpp
• q8csw_linear.cpp -> test_q8csw_linear.cpp

Also add a Buck target for test_q8ta_unary -- the source file existed but no target was defined, leaving the binary unbuildable in fbsource (xplat/executorch/backends/vulkan/test/custom_ops:test_q8ta_unary now resolves).

Updates to references:

• targets.bzl (xplat + fbcode mirrors) -- five define_custom_op_test_binary() call sites renamed; one new entry for test_q8ta_unary.
• CMakeLists.txt (xplat + fbcode mirrors) -- five add_operator_prototype() call sites renamed. test_q8ta_unary is not added to CMake here since it was not in the prior CMake list (existing latent gap; orthogonal to this rename).
• tools/skycastle/.../executorch_vulkan_eureka_unit_tests.sky -- four CI target paths updated. Display labels are also updated to match the binary name (test_q8csw_linear, etc.), consistent with the convention used by adjacent test_q8ta_* entries.
• tools/skycastle/.../executorch_vulkan_gpu_host_unit_tests.sky -- three CI target paths + labels updated (this file does not run q8csw_conv2d).
• fbcode/executorch/oss/.github/workflows/pull.yml + xplat mirror -- five OSS CI references updated, including the build_and_run.sh argument that runs the renamed test_add binary.

Differential Revision: D105059945

[pytorch-bot]

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❌ You can merge normally! (2 Unrelated Failures), 1 Unclassified Failure

As of commit af27deb with merge base 1992bdd ():

UNCLASSIFIED FAILURE - DrCI could not classify the following job because the workflow did not run on the merge base. The failure may be pre-existing on trunk or introduced by this PR:

• Check Labels / Check labels (gh) (this job did not run on the merge base, so DrCI cannot tell whether the failure is pre-existing)

FLAKY - The following job failed but was likely due to flakiness present on trunk:

• pull / unittest-editable / windows / windows-job (gh) (similar failure)
  backends/xnnpack/test/recipes/test_xnnpack_recipes.py::TestXnnpackRecipes::test_8a4w_recipe

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

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

• pull / unittest / windows / windows-job (gh) (trunk failure)
  backends/xnnpack/test/recipes/test_xnnpack_recipes.py::TestXnnpackRecipes::test_8a4w_recipe

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