refactor: remove vae_decode_only context flag (#1653) #2594

Job	Run time
macOS-latest-cmake	9m 32s
windows-latest-cmake-hip	5m 47s
ubuntu-latest-rocm (7.13.0, gfx906;gfx908;gfx90a;gfx942;gfx950;gfx1010;gfx1011;gfx1012;gfx1030;gf...	5m 43s
ubuntu-latest-rocm (7.2.1, gfx908;gfx90a;gfx942;gfx1030;gfx1031;gfx1032;gfx1100;gfx1101;gfx1102;g...	6m 17s
windows-latest-cmake (vulkan, -DSD_VULKAN=ON -DSD_BUILD_SHARED_LIBS=ON)	7m 42s
windows-latest-cmake (avx2, -DGGML_NATIVE=OFF -DGGML_AVX2=ON -DSD_BUILD_SHARED_LIBS=ON)	4m 7s
ubuntu-latest-cmake	7m 0s
windows-latest-cmake (noavx, -DGGML_NATIVE=OFF -DGGML_AVX=OFF -DGGML_AVX2=OFF -DGGML_FMA=OFF -DSD...	3m 58s
windows-latest-cmake (avx512, -DGGML_NATIVE=OFF -DGGML_AVX512=ON -DGGML_AVX=ON -DGGML_AVX2=ON -DS...	3m 46s
Build and push container images (musa, linux/amd64, ubuntu-latest)	52m 41s
Build and push container images (sycl, linux/amd64, ubuntu-latest)	16m 58s
windows-latest-cmake (avx, -DGGML_NATIVE=OFF -DGGML_AVX=ON -DGGML_AVX2=OFF -DSD_BUILD_SHARED_LIBS...	4m 4s
ubuntu-latest-cmake-vulkan	10m 32s
windows-latest-rocm	9m 17s
Build and push container images (cuda, linux/arm64, ubuntu-24.04-arm, -spark, CUDA_VERSION=13.0.0...	17m 32s
windows-latest-cmake (cuda12, -DSD_CUDA=ON -DSD_BUILD_SHARED_LIBS=ON -DCMAKE_CUDA_ARCHITECTURES='...	1h 34m 17s
Build and push container images (vulkan, linux/amd64, ubuntu-latest)	8m 46s
Build and push container images (cuda, linux/amd64, ubuntu-latest)	14m 55s
release	1m 43s
	4h 44m 37s

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