Support PyTorch 2.8.0

[M-Quadra]

Adapt PyTorch 2.8.0 and fix unit tests.

Current failed test cases

coremltools/converters/mil/frontend/torch/test/test_torch_conversion_api.py::TestTorchao::test_weight_only_quantization
coremltools/converters/mil/frontend/torch/test/test_torch_export_conversion_api.py::TestExecuTorchExamples::test_add
coremltools/converters/mil/frontend/torch/test/test_torch_export_conversion_api.py::TestExecuTorchExamples::test_add_mul
coremltools/converters/mil/frontend/torch/test/test_torch_export_conversion_api.py::TestExecuTorchExamples::test_linear
coremltools/converters/mil/frontend/torch/test/test_torch_export_conversion_api.py::TestExecuTorchExamples::test_mul
coremltools/converters/mil/frontend/torch/test/test_torch_export_conversion_api.py::TestExecuTorchExamples::test_softmax
coremltools/converters/mil/frontend/torch/test/test_torch_ops.py::TestActivation::test_selu
coremltools/converters/mil/frontend/torch/test/test_torch_ops.py::TestBatchNorm::test_batchnorm_dynamic_stress
coremltools/converters/mil/frontend/torch/test/test_torch_ops.py::TestEinsum::test_ternary_einsum
coremltools/converters/mil/frontend/torch/test/test_torch_ops.py::TestIndexPut::test_index_put_negative_indices_case_2
coremltools/converters/mil/frontend/torch/test/test_torch_ops.py::TestIndexPut::test_index_put_updates_bool
coremltools/converters/mil/frontend/torch/test/test_torch_ops.py::TestUnfold::test_unfold
coremltools/converters/mil/frontend/torch/test/test_torch_quantization_ops.py::TestPytorchQuantizedOps::test_unpack_int4packed_by_mm_with_eye_matrix
coremltools/converters/mil/frontend/torch/test/test_torch_quantization_ops.py::TestPytorchQuantizedOps::test_weight_int4pack_mm
coremltools/test/optimize/torch/quantization/test_coreml_quantizer.py::test_weight_module_act_fusion

Environment

executorch==0.7.0
├── torch [required: >=2.8.0,<2.9.0, installed: 2.8.0]
└── torchao [required: ==0.12.0, installed: 0.12.0]