opt.nx

opt.nx -- alias stub. Migration to nx_-prefixed canonical name. Consumers via "import \"opt.nx\"" resolve to nx_opt.nx through NishiLang's textual import splicing with path dedup (runtime/import.nx I1). Eliminates duplicate-symbol errors when both names appear in the transitive import tree (e.g., nxc.nx imports opt.nx directly AND nx_regalloc.nx imports nx_opt.nx). Deprecation: delete this stub when every "opt.nx" consumer has migrated to "nx_opt.nx".