phonenumbers

Sync this Go port with a new upstream google/libphonenumber release — regenerate the embedded metadata and reconcile the ported Java logic. Takes an optional argument — `data` (metadata regen only), `code` (code reconciliation only), or empty for both. Use when the user says "sync with upstream", "do an upstream sync", "reconcile against libphonenumber", "pull the latest libphonenumber", bump to a new libphonenumber version, or invokes /sync-upstream. SYNC.md holds the state (baseline version + deliberate divergences); this skill is the procedure.