v3.4.0

eOn 3.4.0

A minor release on v3.3.1. See monorepo CHANGELOG.md section 3.4.0
for the full list.

AKMC on a cluster with CPMD

examples/akmc-cpmd-slurm explores a silicon vacancy with CPMD on four
MPI ranks per search. Each process search is one Slurm job: the client
runs as one process and its ext_pot wrapper starts cpmd.x under
mpirun. On a test node the wrapper's force matched a central finite
difference to 2e-5 eV/A, and the first search returned a process with a
0.029 eV barrier. The ExtPot guide explains how CPMD reports forces:
the table under GRADIENTS (-FORCES) holds forces, and GEOMETRY
carries them at full precision.

Fixes on this path:

• A dimer or process search on a per-image potential such as ext_pot
  evaluated both images on one instance at the same time, with
  parallel = true (the default). Two external programs then shared one
  exchange directory. Each image now keeps its own instance, and an
  error in the second thread stops the job instead of calling
  std::terminate.
• The cluster communicator cancels only the jobs still queued when a
  state reaches its confidence, keeps finished results for harvest, and
  logs a failed cancel. It used to cancel every job and delete the
  scratch directory, results included.
• The MPI communicator no longer stops idle clients when a state reaches
  its confidence.
• The Slurm scripts take the account, partition and job shape from
  EON_SBATCH_ARGS and the client from EON_CLIENT, and list the
  current user's jobs.
• The local communicator kills each client's whole process group, so
  wrappers and their MPI launchers do not outlive the server.
• The MPI potential sends the working directory as int, as the
  MPI_INT it declares, and sleeps mpi_poll_period seconds between
  polls.

pyeonclient

• Linux wheels are manylinux_2_28 and vendor the Fortran and OpenMP
  runtimes, so they install from PyPI and import on a minimal system.
  The bundled rgpot keeps the private SONAME libeon_rgpot.so.3, so a
  pip rgpot wheel imports beside pyeonclient in either order.
• In-process jobs record termination, energy, force calls and job type
  on job_result. LocalInProcess takes a Structure or ConFrame
  and returns saddle and product as frames. In-process jobs poll a
  cancel token between jobs.

Nudged elastic band

• Zoom-NEB packs images onto a window around the climbing image and
  keeps OCI-NEB available on that band.
• The climbing image applies only when an interior image is above both
  endpoints.

Structures and numerics

• Structure matching, rotational matching and space groups go through
  readcon-ops. identical keeps a one-to-one atom map.
• Finite-difference Hessians gain a fourth-order stencil and
  cutoff-colored columns, which take fewer force calls on sparse
  systems.
• Per-atom force norms and periodic wrapping use Highway where it is
  available. NaN forces no longer read as converged.

Build

• The direct in-process rgpot arm is linked on every non-Windows build;
  -Dwith_rgpot is deprecated and ignored. eOn builds against
  rgpot 3.3.0.
• Parameters keeps its state behind a private Impl.
• The pixi environment carries nlohmann_json, so a host copy cannot
  pull /usr/include into a conda build.