support unencrypted sv2

[0xf0xx0]

the spec states encryption is optional for lan and mandatory for remote conns. since we're for home miners, should we have an encryption toggle?

[0xf0xx0]

#1796 (comment)

you've basically got it right on the split, small correction: it's not encryption that's optional on LAN, that part's always on (Noise_NX establishes the session unconditionally). what's optional/mandatory is specifically the auth step - verifying the server cert against the authority pubkey. that's the "optional LAN, mandatory remote" language.