Dlfind restart

[danielguion]

Adds support for DL-FIND checkpoint/restart options in the ASH DL-FIND interface and improves NEB output reporting.

Proposed Changes:

• exposing dump and restart through DLFIND_optimizer
• passing these options through to libdlfind
• preserving existing DL-FIND trajectory files when restarting
• reconstructing ASH-side NEB bookkeeping on restart from existing trajectory files
• checking that all expected NEB images are available before writing a new path
• writing DLFIND_NEBpath_current.xyz atomically via a temporary file
• reporting NEB cycle/image information in geometry output
• flushing NEB progress messages to improve output ordering

I tested the restart workflow by interrupting and resuming a DL-FIND NEB calculation, and it worked successfully.

The changes here are based on the NEW branch.

[RagnarB83]

Looks great. Thanks for contributing.