Isolate AMS from PyTorch

[lpottier]

This PR aims at removing PyTorch from the critical path in AMS. The strict dependency on PyTorch prevents AMS from being used in some multi-physics codes and thus must be removed. This PR introduces the CMake flag -DWITH_TORCH=[On|Off].

This PR replaces Torch tensors with AMSTensor when possible. By default, -DWITH_TORCH=On, when AMS is compiled with Torch we can perform inference but when we do not compile AMS with Torch we can still store physics and it acts as a training only mode.

TODO:

• Remove Torch dependency in evaluate()
• Adapt tests to the no torch path
• Test with RabbitMQ backend

[github-actions]

Cpp-Linter Report ⚠️

Some files did not pass the configured checks!

clang-tidy (v18.1.8) reports: 8 concern(s)

• src/AMSlib/include/SmallVector.hpp:227:53: warning: [clang-diagnostic-unused-parameter]

  unused parameter 'Elt'

    227 |   void assertSafeToReferenceAfterResize(const void* Elt, size_t NewSize)
        |                                                     ^

• src/AMSlib/include/SmallVector.hpp:227:65: warning: [clang-diagnostic-unused-parameter]

  unused parameter 'NewSize'

    227 |   void assertSafeToReferenceAfterResize(const void* Elt, size_t NewSize)
        |                                                                 ^

• src/AMSlib/wf/hdf5db.cpp:38:20: warning: [clang-diagnostic-unused-function]

  unused function 'tensorSizeToString'

     38 | static std::string tensorSizeToString(ArrayRef<AMSTensor::IntDimType> shape)
        |                    ^~~~~~~~~~~~~~~~~~

• tests/AMSlib/ams_interface/ams_ete_env.cpp:88:30: warning: [clang-diagnostic-vla-cxx-extension]

  variable length arrays in C++ are a Clang extension

     88 |             const DType* ins[num_inputs];
        |                              ^~~~~~~~~~
  /home/runner/work/AMS/AMS/tests/AMSlib/ams_interface/ams_ete_env.cpp:87:59: note: while substituting into a lambda expression here
     87 |               ams::SmallVector<ams::AMSTensor>& ams_outs) {
        |                                                           ^
  /home/runner/work/AMS/AMS/tests/AMSlib/ams_interface/ams_ete_env.cpp:178:12: note: in instantiation of member function 'Problem<float>::ams_run' requested here
    178 |       prob.ams_run(wf, resource, num_iterations, avg_elements);
        |            ^
  /home/runner/work/AMS/AMS/tests/AMSlib/ams_interface/ams_ete_env.cpp:88:30: note: implicit use of 'this' pointer is only allowed within the evaluation of a call to a 'constexpr' member function
     88 |             const DType* ins[num_inputs];
        |                              ^

• tests/AMSlib/core/amstensor_torch_benchmark.cpp:77:19: error: [clang-diagnostic-error]

  use of undeclared identifier 'AMS_TENSOR_BENCHMARK_CSV_DEFAULT'

     77 |                 : AMS_TENSOR_BENCHMARK_CSV_DEFAULT;
        |                   ^

• tests/AMSlib/core/amstensor_torch_benchmark.cpp:93:56: error: [clang-diagnostic-error]

  use of undeclared identifier 'AMS_BENCHMARK_GIT_COMMIT'

     93 |     _output << csvField(_timestamp) << ',' << csvField(AMS_BENCHMARK_GIT_COMMIT)
        |                                                        ^

• tests/AMSlib/core/amstensor_torch_benchmark.cpp:94:32: error: [clang-diagnostic-error]

  use of undeclared identifier 'AMS_BENCHMARK_SOURCE_STATE'

     94 |             << ',' << csvField(AMS_BENCHMARK_SOURCE_STATE) << ','
        |                                ^

• tests/AMSlib/perf_regression/ams_bench_db.cpp:2:10: error: [clang-diagnostic-error]

  'mpi.h' file not found

      2 | #include <mpi.h>
        |          ^~~~~~~

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