Delete deprecated PlainLayout, PlainAQTTensorImpl and related v1 code paths

[jerryzh168]

Stack from ghstack (oldest at bottom):

• -> Delete deprecated PlainLayout, PlainAQTTensorImpl and related v1 code paths #4151
• Delete deprecated TensorCoreTiledLayout and related code #4153
• Move bitpacking.py to prototype and add uintx_utils.py #4152

• Remove PlainLayout class from dtypes/utils.py
• Delete torchao/dtypes/uintx/plain_layout.py
• Remove int8 weight and int8 dynamic activation dispatch from AQT dispatch table
• Remove AQT embedding dispatch (used PlainAQTTensorImpl)
• Change Int8WeightOnlyConfig default to version=2 (removes v1 AQT path)
• Change Int8DynamicActivationInt8WeightConfig default to version=2 (removes v1 AQT path)
• Remove PlainLayout from public exports
• Update tests to use v2 tensor types

[pytorch-bot]

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❌ 12 New Failures

As of commit 218106c with merge base 1f90b4d ():

NEW FAILURES - The following jobs have failed:

• Build Docs / build_docs (3.11) (gh)
• Run 1xH100 Tests / test (H100, linux.aws.h100, --pre torch torchvision torchaudio mslk --index-url https://download.... / linux-job (gh)
  test/integration/test_integration.py::TestWeightOnlyInt8Quant::test_weight_only_groupwise_quant
• Run 1xL4 Tests / test (SM-89, linux.g6.4xlarge.experimental.nvidia.gpu, --pre torch --index-url https://download.p... / linux-job (gh)
  test/integration/test_integration.py::TestWeightOnlyInt8Quant::test_weight_only_groupwise_quant
• Run Regression Tests / test (CPU 2.10, linux.4xlarge, torch==2.10.0 --index-url https://download.pytorch.org/whl/cpu, cpu) / linux-job (gh)
  RuntimeError: Command docker exec -t 54c0a9a3ca11fcd2a16a029649d28abf2df1eb68e9ee0a19956a957bd6e8e58b /exec failed with exit code 2
• Run Regression Tests / test (CPU 2.8, linux.4xlarge, torch==2.8.0 --index-url https://download.pytorch.org/whl/cpu, cpu) / linux-job (gh)
  RuntimeError: Command docker exec -t 0b4cde0dca882dc32dba0785d47f71b9201b1cc51fa51b1c855e7cbcb331c949 /exec failed with exit code 2
• Run Regression Tests / test (CPU 2.9, linux.4xlarge, torch==2.9.1 --index-url https://download.pytorch.org/whl/cpu, cpu) / linux-job (gh)
  RuntimeError: Command docker exec -t 4906cbe3b98817d86105219bd4edbd3d950e76586b28fb116c329438df217ed0 /exec failed with exit code 2
• Run Regression Tests / test (CUDA 2.10, linux.g5.12xlarge.nvidia.gpu, torch==2.10.0, cuda, 12.6) / linux-job (gh)
  RuntimeError: Command docker exec -t 9240398250a26f98daf095ba72164c24b023e541227669a8885914681ad4a9e3 /exec failed with exit code 2
• Run Regression Tests / test (CUDA 2.8, linux.g5.12xlarge.nvidia.gpu, torch==2.8.0, cuda, 12.6) / linux-job (gh)
  RuntimeError: Command docker exec -t 31c73bdba2ceed8fe3975e8c7246edaea36ca2ce93d6cc7271b497ff61fdbd0b /exec failed with exit code 2
• Run Regression Tests / test (CUDA 2.9, linux.g5.12xlarge.nvidia.gpu, torch==2.9.1, cuda, 12.6) / linux-job (gh)
  RuntimeError: Command docker exec -t 7aa2fe71c6d2674a38f0b2dce2906a910c93edd2cf9419e201ed5f16d23eff15 /exec failed with exit code 2
• Run Regression Tests / test-nightly (CPU Nightly, linux.4xlarge, --pre torch --index-url https://download.pytorch.org/wh... / linux-job (gh)
  RuntimeError: Command docker exec -t 3ed207177f0ecf0878dc0e5b2eb6abe3a9a5c52284e5d327feb07a3c447021f8 /exec failed with exit code 2
• Run Regression Tests / test-nightly (CUDA Nightly, linux.g5.12xlarge.nvidia.gpu, --pre torch --index-url https://downloa... / linux-job (gh)
  RuntimeError: Command docker exec -t 3e6c6a1071213c5dae113e55377efd31ae886b8e464927a83fbebc5ab82b5705 /exec failed with exit code 2
• Run TorchAO Experimental MPS Tests / test-mps-ops / macos-job (gh)
  RuntimeError: Command bash /Users/ec2-user/runner/_work/_temp/exec_script failed with exit code 2

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[andrewor14]

Technically these were only deprecated recently (as of #4074). We can still delete them now, just want to point out it hasn't been 1 release yet

[jerryzh168]

Technically these were only deprecated recently (as of #4074). We can still delete them now, just want to point out it hasn't been 1 release yet

I think it's fine since the v1 config has been deprecated for a long time