fix: SpkIterator::new_with_range takes wildcards..

..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
```

crates/chain/tests/test_keychain_txout_index.rs

@@ -384,4 +384,12 @@ fn test_non_wildcard_derivations() {
         txout_index.reveal_to_target(&TestKeychain::External, 200);
     assert_eq!(revealed_spks.count(), 0);
     assert!(revealed_changeset.is_empty());
+
+    // we check that spks_of_keychain returns a SpkIterator with just one element
+    assert_eq!(
+        txout_index
+            .spks_of_keychain(&TestKeychain::External)
+            .count(),
+        1,
+    );
 }