validateExtendedPublicKey needs SLIP132 and regtest

[destrys]

currently, validateExtendedPublicKey only checks for xpub and tpub for networks mainnet and testnet.

Caravan configs currently only export xpubs/tpubs, so if only validates those on reading a config, but when we make Caravan smart enough to read other wallet configs, it will be better to validate the Ypub/Zpub etc instead of converting everything to an xpub first.

And generally, unchained-bitcoins should be SLIP132 aware at a minimum.

Additionally, we should support a REGTEST network type so the apps don't have to change to specify TESTNET even though they are on regtest.

[jevidon]

Migrated issue to new repo: caravan-bitcoin/caravan#61