Scf convergence migration

[JFRudzinski]

Implemented SCF convergence migration across all target parsers (abinit, ams, crystal, exciting, fhiaims, gpaw, quantumespresso, vasp) to the new workflow + scf_steps model.

High-level changes:

• Ported parser-specific SCF iteration signals into outputs.scf_steps (energy deltas, energies, durations, and code-specific SCF metadata where available).
• Populated new workflow convergence targets in workflow2 (SinglePoint, GeometryOptimization, and MD where relevant), including SCF and geometry thresholds.
• Updated parser schema mappings to expose the new scf_steps fields and avoid duplicated/legacy convergence storage.
• Added/extended parser tests with explicit assertions on:
  • workflow type/method and convergence target thresholds/types
  • SCF-step quantity presence, lengths, and representative values
• Updated migration documentation (SCF_CONVERGENCE_MIGRATION.md) with per-parser status, approach, caveats, and test outcomes.

Net result:

• Convergence information now follows one consistent structure across parsers, aligned with the refactored schema and NOMAD unit handling semantics.

depends on FAIRmat-NFDI/nomad-simulations#260

[JFRudzinski]

Here are the implementation notes:

SCF_CONVERGENCE_MIGRATION.md