ROM method tables used static mrb_mt_tbl variables shared
across the process. The next pointer in each wrapper was
mutated by mrb_mt_init_rom(), causing cross-state
contamination when multiple mrb_state instances existed.
Allocate mrb_mt_tbl wrappers per-state via mrb_malloc().
The const mrb_mt_entry[] arrays remain static and shared.
Wrappers are tracked in mrb->rom_mt and freed at mrb_close().
Remove MRB_MT_ROM_TAB macro; add MRB_MT_INIT_ROM macro that
auto-computes size and calls the new mrb_mt_init_rom().
Co-authored-by: Claude <noreply@anthropic.com>
Yukihiro "Matz" Matsumoto
71cb3c2e3a