feat: add MACE interface

[FelyCZ]

Add MACE Interface via MPI

Description

This PR adds a new interface for the MACE (Machine Learning Atomic Cluster Expansion) potential to ABIN. MACE is integrated via an MPI-based client-server architecture: a Python server loads and evaluates the MACE ML model, while the Fortran side communicates coordinates, energies, and forces over MPI. This follows the same pattern used for the existing TeraChem (_tera_) interface.

The interface supports configurable model paths, device selection (CPU/CUDA), precision settings, and various MACE-specific options -- all controlled through a new &mace namelist in the ABIN input file.

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File Changes

Fortran Core

File	Description
src/mace_mpi_api.F90	[NEW] Core MPI API module (mod_mace_mpi). Handles MPI port connection to the Python server, sends atom types/config/coordinates, and defines all MACE namelist variables (model path, device, dtype, batch size, etc.).
src/force_mace.F90	[NEW] Force driver module (mod_force_mace). Orchestrates per-bead force evaluation -- sends coordinates via send_mace, receives energy and forces via receive_mace. Supports OpenMP.
src/forces.F90	Added _mace_ case to the force_wrapper potential selector, routing to force_mace().
src/init.F90	Added &mace namelist reading and MACE interface/server initialization when pot='_mace_'.
src/mpi_wrapper.F90	Added _mace_ to the MPI-required potential check so non-MPI builds raise a clear error.
src/Makefile	Added mace_mpi_api.o and force_mace.o to the build.

Python Server

File	Description
interfaces/MACE/mace_server.py	[NEW] MACE MPI server. Opens MPI port, accepts connection from ABIN, receives configuration and atom data, loads the MACE model, and returns energies/forces each step. Handles unit conversions (Bohr <-> Å, Hartree <-> eV) and supports foundation model auto-download.
interfaces/MACE/README.md	[NEW] Documentation covering requirements, manual/automatic launch instructions, and a full configuration reference table for all &mace namelist parameters. Includes MACE-OFF licensing notice.
interfaces/MACE/MACE-OFF23_medium.model	[NEW] Bundled pre-trained MACE-OFF23 medium model (~18 MB) for out-of-the-box usage. Licensing notice is included in the README.

Tests

File	Description
tests/MACE/test.sh	[NEW] Integration test script. Launches the mock MACE server and ABIN via MPI, runs a short MD simulation, and validates output against reference files.
tests/MACE/mock_mace_server.py	[NEW] Mock MACE server for testing. Implements the same MPI protocol as the real server but returns forces from a simple harmonic potential, avoiding the need for mace-torch/PyTorch.
tests/MACE/input.in	[NEW] Test input file with pot='_mace_' and &mace namelist.
tests/MACE/mini.xyz	[NEW] Test geometry (water molecule).
tests/MACE/*.ref	[NEW] Reference output files (energies.dat.ref, forces.xyz.ref, movie.xyz.ref, velocities.xyz.ref, temper.dat.ref).
tests/test.sh	Registered MACE in the MPI test folder list.
unit_tests/test_mace.pf	[NEW] pFUnit tests verifying default namelist values, MPI tag constants, and non-MPI error handling.
unit_tests/Makefile	Added mace target to the unit test build, test runner, and clean targets.

Utilities & Docs

File	Description
utils/run.mace_mpi_abin.sh	[NEW] Launch script that starts both the MACE Python server and ABIN, connects them via MPI, and monitors both processes with automatic cleanup.
dev_scripts/install_mace.sh	[NEW] Convenience script to clone the MACE repo and install dependencies (mace-torch, mpi4py).
sample_inputs/input.in.mace	[NEW] Sample input file demonstrating &mace namelist configuration.
README.md	Added MACE to the list of optional libraries with a brief description and install reference.