B20 Authenticity Check

🆕 Run FIRST on any 'B20'. A scammer can deploy a normal contract at a vanity 0xB200… address and fake the whole B20 read surface — the B20Factory precompile is the one authority that can't be spoofed. Verifies factory registration + bytecode absence (real B20s are chain-native precompiles with no code). verdict: genuine / fake_lookalike / not_b20. The 2-cent check that keeps every other B20 answer honest.