ci : run test-backend-ops as a dedicated ci/run.sh test (#28740)

* ci : run test-backend-ops as a dedicated gg test

Run test-backend-ops as a separate gg test in ci/run.sh so it is executed outside ctest. With GG_BUILD_HIGH_PERF it keeps the existing CPU-only invocation (-b CPU); otherwise it runs all available backends without a backend filter.

Remove the dedicated backend-ops workflow and keep test-backend-ops as a built target that is not registered with ctest to avoid duplicate runs.

Assisted-by: pi:llama.cpp/DeepSeek-V4-Flash-Vision-Exp

* ci : run test-backend-ops earlier and enable high-perf on kleidiai

Move the test-backend-ops gg test before test-llama-archs.

Enable GG_BUILD_HIGH_PERF and LLAMA_ARG_THREADS on the Graviton4 KleidiAI job and use the standard self-hosted results/mnt paths.

Add TODO markers for decoupling tests from libllama.

Assisted-by: pi:llama.cpp/DeepSeek-V4-Flash-Vision-Exp

* ci : run test-backend-ops in parallel

Pass -j $(nproc) to test-backend-ops in both high-perf and all-backend modes.

Assisted-by: pi:llama.cpp/DeepSeek-V4-Flash-Vision-Exp

* ci : disable parallel tests for ROCm

* cont : disable parallel tests with MoltenVK

.github/workflows/build-webgpu.yml

@@ -190,6 +190,4 @@ jobs:
         id: cmake_test
         run: |
           cd build
-          # This is using llvmpipe and runs slower than other backends
-          # test-backend-ops is too slow on llvmpipe, skip it
-          ctest -L main -E test-backend-ops --verbose --timeout 900
+          ctest -L main --verbose --timeout 900