fix!: return errors from Wallet.peek_address

Change `Wallet.peek_address` to return errors for out of range derivation indexes and descriptors that cannot produce an address (instead of allowing upstream `expect()` calls to panic)

Start at the Wallet.peek_address entry point and trace how out-of-range derivation indexes and descriptors that cannot produce an address are handled. Done means both cases return errors to callers instead of reaching upstream expect() calls and panicking; run the relevant existing tests or add coverage for these two cases.

Written by the indexing model from the issue text.