Add new search algorithm

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Pull request overview

This PR introduces a new neighbor-list based search implementation under module_neighlist and wires it into the Lennard-Jones (LJ) ESolver path, alongside new unit tests and build-system integration.

Changes:

• Added module_neighlist (neighbor search + binning + neighbor list allocator) and corresponding unit tests.
• Introduced an IAtomProvider interface and made UnitCell implement it.
• Switched ESolver_LJ::runner from the existing module_neighbor search path to the new NeighborSearch path.

Reviewed changes

Copilot reviewed 20 out of 20 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
source/source_md/test/CMakeLists.txt	Adds new neighlist sources to MD test dependencies.
source/source_esolver/esolver_lj.h	Declares UnitCellPlus conversion helper used by the new neighbor search path.
source/source_esolver/esolver_lj.cpp	Replaces old grid-based neighbor search with NeighborSearch usage in LJ runner.
source/source_cell/unitcell.h	Makes UnitCell implement IAtomProvider for neighbor search consumption.
source/source_cell/module_neighlist/unitcell_plus.h	Adds a lightweight test-friendly IAtomProvider implementation.
source/source_cell/module_neighlist/unitcell_interface.h	Adds IAtomProvider abstraction for atom/lattice queries.
source/source_cell/module_neighlist/neighbor_search.h	Declares the new neighbor search API and data members.
source/source_cell/module_neighlist/neighbor_search.cpp	Implements neighbor search initialization, expansion, and neighbor building.
source/source_cell/module_neighlist/neighbor_list.h	Adds a simple page allocator + neighbor list storage type.
source/source_cell/module_neighlist/neighbor_atom.h	Adds NeighborAtom and InputAtoms structures used by the algorithm.
source/source_cell/module_neighlist/bin_manager.h	Declares binning and neighbor construction helper.
source/source_cell/module_neighlist/bin_manager.cpp	Implements bin construction, binning, and neighbor list building.
source/source_cell/module_neighlist/CMakeLists.txt	Adds neighbor_search object library and conditional tests subdir.
source/source_cell/module_neighlist/test/CMakeLists.txt	Adds new test targets for neighlist components.
source/source_cell/module_neighlist/test/neighbor_search_test.cpp	Adds unit tests for NeighborSearch behavior/branches.
source/source_cell/module_neighlist/test/neighbor_list_test.cpp	Adds unit tests for PageAllocator and NeighborList.
source/source_cell/module_neighlist/test/bin_manager_test.cpp	Adds unit tests for BinManager behavior and edge cases.
source/source_cell/CMakeLists.txt	Adds module_neighlist subdirectory to the cell build.
source/Makefile.Objects	Adds neighlist objects to Makefile-based build.
CMakeLists.txt	Links the new neighbor_search object library into the main target.

Comments suppressed due to low confidence (1)

source/source_cell/module_neighlist/neighbor_search.cpp:65

• NeighborSearch::init hard-codes mpi_size = 1 while still accepting mpi_rank. For mpi_rank != 0 this produces invalid (x,y,z) decomposition and incorrect inside/ghost selection. Either pass mpi_size into init (or query it from an MPI communicator) and validate 0 <= mpi_rank < mpi_size, or remove the MPI-rank parameters until multi-rank decomposition is actually supported.

    int mpi_size = 1;
    int nx, ny, nz;
    decompose(mpi_size, nx, ny, nz);

    z = mpi_rank / (nx * ny);
    y = (mpi_rank % (nx * ny)) / nx;
    x = mpi_rank % (nx * ny) % nx;

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