Regenerate benchmark_params.pkl after aca-data cross + pre-65 health fixes.

Picks up the validated cross-grid (`health_trans_cross`) and same-grid
pre-65 (`health_trans_pre65`) transition matrices that now carry valid
probability rows at every source-active age (51-64).

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

Author: hmgaudecker