fix network conversions

[zkao]

e.g.

impl From<farcaster_core::blockchain::Network> for monero::Network {
    fn from(network: farcaster_core::blockchain::Network) -> Self {
        match network {
            blockchain::Network::Mainnet => monero::Network::Mainnet,
            blockchain::Network::Testnet => monero::Network::Stagenet,
            blockchain::Network::Local => monero::Network::Mainnet,
        }
    }
}

[zkao]

blockchain::Network::Local should map to monero::Network::Mainnet