feat: partition the bdd flow and fix its exponential blowups

• convert_bdd builds one BuDDy diagram per partition block, with the same -n / -g options as convert_bbdd, plus -t, -c and -o
• create_bdd memoises converted gates; reconvergent fanout was rebuilt once per path
• the blif writer and the height walk visit each node once instead of once per path (c432 wrote 18.3M .names lines for 1850 nodes)
• bdd_printtable only runs under DEBUG_BDD

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>