Solve the OG-Core steady state serially in the worker

[error9098x]

Summary

• What changed:
  • _solve() in API/Classes/OGCore/ogc_worker.py runs OG-Core's steady-state solve without a dask client, by wrapping SS.run_SS for the duration of the run and restoring it afterwards.
  • A dask client is created only for transition-path runs, with the dashboard disabled so a run never binds an extra port.
  • Closing the client is skipped when none was created.
• Why: OG-Core 0.20.0 re-sends the full model parameters to every dask worker on each steady-state iteration (Dask client handling in TPI/SS: unguarded scatter breaks serial runs; SS re-scatters params every residual evaluation PSLmodels/OG-Core#1211). The upstream fix (Scatter SS parameters once per solve instead of per residual evaluation PSLmodels/OG-Core#1214) is only in v0.20.1, and the country calibrations still lock ogcore==0.20.0. This workaround can be removed once they move to >= 0.20.1.

Linked issue (if applicable)

• Closes [Bug] Steady-state solve re-sends model parameters to every dask worker on each iteration (OG-Core 0.20.0) #552

Validation

• Tests: not applicable. The worker imports ogcore, which the MUIOGO test suite does not install. uv run ruff check . passes and uv run pytest passes (358 passed, 2 skipped) on this branch.
• Manual verification: ran the worker's run mode directly with OG-PHL's interpreter (ogcore 0.20.0) on two copies of the same real steady-state baseline (macOS 26.5.1, 10 cores):
  • main: stalled. After ~4 minutes the log had repeated the same 9 GE loop errors lines 34 times with no progress; the run was stopped.
  • this branch: completed in 31 seconds (exit 0, SS_vars.pkl written).
  • Transition path on this branch, same baseline: completed in 431 seconds (exit 0, TPI_vars.pkl written).

Checklist

• Change is scoped — no unrelated refactors
• Branched from main; PR targets EAPD-DRB/MUIOGO:main
• Docs updated for any setup, workflow, or architecture change (not applicable)

Notes for reviewers

• execute.runner calls SS.run_SS through the module (ogcore/execute.py:46), so wrapping it takes effect. OG-Core 0.20.0's run_TPI calls client.scatter without checking for a client (TPI.py:969), which is why transition-path runs still get one.
• Upstream keeps the steady state parallel and only sends the parameters once; this workaround makes it serial instead.