Optimize pair-restricted and high-MOI JAX fitting

[logan-blaine]

Summary

• add exact pair-restricted fitting via --pairs-to-test
• avoid unnecessary high-MOI guide-matrix retention for shared effects
• compile minibatched SVI updates with lax.scan
• assemble restricted beta parameters into dense matrices for fast high-MOI GEMMs
• add coverage for pair restriction and high-MOI workflows

Validation

• targeted pair/high-MOI/API tests pass
• full non-fitted-workflow test suite passes
• Gasperini TSS/NTC pilot completed successfully
• Docker workflow dispatched separately on this branch