refactor HF reference config and pretrain defaults

[AllanChain]

• Move HF reference settings from system.* to pretrain.reference.* so the system block stays physics-only.
• Support specifying PySCF verbosity and other parameters.
• Default HF is unrestricted (UHF/KUHF) unless the method selects RHF/KRHF.
• Use HF distribution for pretraining by default.
• Use a constant learning rate for pretraining by default.
• Solid evaluation includes reference.* configs because HF is needed to get k-points.
• Handle empty spin blocks in slogdet for SCF wavefunctions.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 89.18919% with 8 lines in your changes missing coverage. Please review.
✅ Project coverage is 86.48%. Comparing base (786f080) to head (f42a0a2).
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
src/jaqmc/app/solid/workflow.py	76.47%	2 Missing and 2 partials ⚠️
src/jaqmc/utils/atomic/scf.py	81.81%	2 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #27      +/-   ##
==========================================
+ Coverage   86.38%   86.48%   +0.09%     
==========================================
  Files         125      125              
  Lines        5650     5690      +40     
  Branches      522      527       +5     
==========================================
+ Hits         4881     4921      +40     
+ Misses        560      557       -3     
- Partials      209      212       +3     

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