B20 Access Type

🆕 A B20 transfer policy is either a BLOCKLIST (allowed unless listed) or an ALLOWLIST (allowed ONLY if listed — a permissioned/whitelist token you can't even receive uninvited). b20-safety flags that a policy exists; this decodes its TYPE per scope (send/receive/execute/mint) — the difference between 'the issuer can block bad actors' and 'this is a permissioned RWA you can't hold uninvited'.