Require valid states for SPECTRE physical losses

[krystophny]

Prevents numerical failures or non-finite interface states from becoming physical loss events.

• only OUTSIDE_DOMAIN can seed an outer-boundary landing
• validate landed coordinates, momentum, pitch, B, mu, and refraction radicand
• return CROSS_INVALID and roll back into recovery instead of logging a loss
• apply the same validity contract to RK SPECTRE stepping
• adversarial NaN and invalid-momentum tests

The complete stacked branch passes the full fo static, build, test, and lint pipeline.