Fixes the two sp(KEY,KEY) extended key examples:
- The watch-only example's scan
xprvwas at the account level, so it could derive the spend private key, and its spendxpub.../0hrequired hardened derivation from a public key. - Neither example used the BIP352 child paths (
1h/0scan,0h/0spend).
The watch-only example now places the scan xprv at .../1h and the spend xpub at .../0h. The full-wallet example uses the account xprv with /1h/0 and /0h/0.