Refactor: Remove the ML training code

[sunliang98]

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Linked Issue

Fix #7091

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What's changed?

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[Copilot]

Pull request overview

Removes the standalone ML training toolchain under module_ofdft/ml_tools (issue #7091) while keeping the runtime NN model used by ML-KEDF/ML-EXX, relocating it to module_ofdft/nn_of.{h,cpp} and updating includes/build wiring accordingly.

Changes:

• Deleted ML training executable sources and helper modules (train_kedf, data, input, kernel, grid, pauli_potential, and ml_tools/CMakeLists.txt).
• Added/relocated the libtorch NN module implementation to source_pw/module_ofdft/nn_of.{h,cpp}.
• Updated include paths and CMake source lists to reference the new NN module location.

Reviewed changes

Copilot reviewed 17 out of 19 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
source/source_pw/module_ofdft/nn_of.h	Adds NN module header (now used by runtime ML code).
source/source_pw/module_ofdft/nn_of.cpp	Adds NN module implementation (forward pass, layer registration).
source/source_pw/module_ofdft/ml_tools/train_kedf.h	Removes training driver API.
source/source_pw/module_ofdft/ml_tools/train_kedf.cpp	Removes training loop implementation.
source/source_pw/module_ofdft/ml_tools/pauli_potential.h	Removes training-time Pauli potential implementation.
source/source_pw/module_ofdft/ml_tools/pauli_potential.cpp	Removes training-time Pauli potential implementation.
source/source_pw/module_ofdft/ml_tools/main.cpp	Removes standalone training executable entrypoint.
source/source_pw/module_ofdft/ml_tools/kernel.h	Removes training-time kernel utilities.
source/source_pw/module_ofdft/ml_tools/kernel.cpp	Removes training-time kernel utilities.
source/source_pw/module_ofdft/ml_tools/input.h	Removes training input parser/config.
source/source_pw/module_ofdft/ml_tools/input.cpp	Removes training input parser/config.
source/source_pw/module_ofdft/ml_tools/grid.h	Removes training-time FFT grid utilities.
source/source_pw/module_ofdft/ml_tools/grid.cpp	Removes training-time FFT grid utilities.
source/source_pw/module_ofdft/ml_tools/data.h	Removes training dataset loader.
source/source_pw/module_ofdft/ml_tools/data.cpp	Removes training dataset loader.
source/source_pw/module_ofdft/ml_tools/CMakeLists.txt	Removes separate nnof training build.
source/source_pw/module_ofdft/ml_base.h	Updates NN include path to new location.
source/source_pw/module_ofdft/CMakeLists.txt	Updates ML-KEDF object sources to compile nn_of.cpp from new location.
source/source_estate/module_pot/pot_ml_exx.h	Updates NN include path to new location for ML-EXX.

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[mohanchen]

LGTM