The wallet is currently created without setting any lookahead value for
the keychain. This implicitly makes it a lookahead of 0. As this is a
high-level interface we should avoid footguns and aim for a reasonable
default.
Instead of simply patching it for wallet, we alter `KeychainTxOutIndex`
to have a default lookahead value. Additionally, instead of a
per-keychain lookahead, the constructor asks for a `lookahead` value.
This avoids the footguns of having methods which allows the caller the
decrease the `lookahead` (and therefore panicing). This also simplifies
the API.
Co-authored-by: Antoine Poisot <darosior@protonmail.com>
Co-authored-by: 志宇 <hello@evanlinjin.me>
..into account
When you pass a non-wildcard descriptor in `new_with_range`, we make
sure that the range length is at most 1; if that's not the case, we
shorten it.
We would previously use `new_with_range` without this check and with a
non-wildcard descriptor in `spks_of_all_keychains`, this meant creating
a spkiterator that would go on producing the same spks over and over
again, causing some issues with syncing on electrum/esplora.
To reproduce the bug, run in `example-crates/example_electrum`:
```
cargo run "sh(wsh(or_d(c:pk_k(cPGudvRLDSgeV4hH9NUofLvYxYBSRjju3cpiXmBg9K8G9k1ikCMp),c:pk_k(cSBSBHRrzqSXFmrBhLkZMzQB9q4P9MnAq92v8d9a5UveBc9sLX32))))#zp9pcfs9" scan
```
SpkIterator was created with its own nth() and next() implementations
and its own new() and new_with_range() constructors.
Co-authored-by: 志宇 <hello@evanlinjin.me>
