Do not restore constant_buffer, and use bytes instead of Buffer

[lucylq]

Stack from ghstack (oldest at bottom):

• -> Do not restore constant_buffer, and use bytes instead of Buffer #15802
• Use PTEFile class in serialize_pte_binary #15801
• Introduce PTEFile class #15800

All constants are serialized in the segment (none in the Program).

This PR:

1. Places constant data into the PTEFile class instead of restoring it into the Program.
2. Use List[bytes] instead of List[Buffer] for constant and mutable data. Buffer was initially used to maintain alignment; now, constants are serialized with alignment in the segment, and Buffer is not required.

Update tests.

After this, we can mark 'constant_buffer' as deprecated, as it's no longer being used in deserialization or emitter.

Differential Revision: D86913756

[pytorch-bot]

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❌ 14 New Failures, 2 Unrelated Failures

As of commit 0b2ffea with merge base 7600df8 ():

NEW FAILURES - The following jobs have failed:

• Lint / lintrunner / linux-job (gh)
  >>> Lint for exir/verification/interpreter.py:
• Lint / lintrunner-mypy / linux-job (gh)
  >>> Lint for backends/arm/test/misc/test_call_operator_submodule.py:
• pull / test-moshi-linux / linux-job (gh)
  RuntimeError: Command docker exec -t ca690051eaec7479dc73dd56c79bb546ff65e5bba730129e871e39867703cd9f /exec failed with exit code 1
• pull / unittest / macos / macos-job (gh)
  backends/xnnpack/test/test_xnnpack_partitioner.py::TestXnnpackPartitioner::test_multi_method_partitioning_with_shared_weights
• pull / unittest-editable / macos / macos-job (gh)
  backends/xnnpack/test/test_xnnpack_partitioner.py::TestXnnpackPartitioner::test_multi_method_partitioning_with_shared_weights
• Test CUDA Builds / test-model-cuda-e2e (google, gemma-3-4b-it, non-quantized) / linux-job (gh)
  RuntimeError: Command docker exec -t d18c1c5766387bdf1dfd9a265b6f921f4dc6391f3c4efe8b04484eca40a9f463 /exec failed with exit code 1
• Test CUDA Builds / test-model-cuda-e2e (google, gemma-3-4b-it, quantized-int4-tile-packed) / linux-job (gh)
  RuntimeError: Command docker exec -t 0ae40fb6e09e057aa4080a100683fd39f73b82c2617c65bf0a87acf47e00d361 /exec failed with exit code 1
• Test CUDA Builds / test-model-cuda-e2e (mistralai, Voxtral-Mini-3B-2507, quantized-int4-weight-only) / linux-job (gh)
  RuntimeError: Command docker exec -t b858047fe476214ac823468029effc36c88548a5cef5c6bde10923ad940be335 /exec failed with exit code 1
• Test CUDA Builds / test-model-cuda-e2e (openai, whisper-large-v3-turbo, non-quantized) / linux-job (gh)
  RuntimeError: Command docker exec -t 4e409d247e7a9d8240941b05bfeae50dc855f2535708463aa642e3fa46b60403 /exec failed with exit code 1
• Test CUDA Builds / test-model-cuda-e2e (openai, whisper-large-v3-turbo, quantized-int4-tile-packed) / linux-job (gh)
  RuntimeError: Command docker exec -t bae89b67a42ec5b06f68135689e687b6f0fb3a6637991dbc03cc0febd8007bd7 /exec failed with exit code 1
• Test CUDA Builds / test-model-cuda-e2e (openai, whisper-large-v3-turbo, quantized-int4-weight-only) / linux-job (gh)
  RuntimeError: Command docker exec -t d77d46d86029942cabb4720794cb2d2192cc9c1a3c18484a5928e5d04b4fd541 /exec failed with exit code 1
• Test CUDA Builds / test-model-cuda-e2e (openai, whisper-small, non-quantized) / linux-job (gh)
  RuntimeError: Command docker exec -t eec85834388c6cb46460e8434a5be4afb421b489d40fd363250ffd4a60ea0885 /exec failed with exit code 1
• Test CUDA Builds / test-model-cuda-e2e (openai, whisper-small, quantized-int4-tile-packed) / linux-job (gh)
  RuntimeError: Command docker exec -t 80d54a015275d92f926660ea7c1b2f34f5a21fb4136b4f8c8d34e7c30838e2c0 /exec failed with exit code 1
• Test CUDA Builds / test-model-cuda-e2e (openai, whisper-small, quantized-int4-weight-only) / linux-job (gh)
  RuntimeError: Command docker exec -t 09a496f4cd3c1202474b45a66f278d9002d970dcc0a9d203fd5a215af8e537bb /exec failed with exit code 1

FLAKY - The following jobs failed but were likely due to flakiness present on trunk:

• pull / unittest / linux / linux-job (gh) (detected as infra flaky with no log or failing log classifier)
• pull / unittest-editable / linux / linux-job (gh) (detected as infra flaky with no log or failing log classifier)

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