chore: extract TestEnv into separate crate

`TestEnv` is extracted into its own crate to serve as a framework
for testing other block explorer APIs.

crates/electrum/src/electrum_ext.rs

@@ -189,7 +189,7 @@ impl<A: ElectrumApi> ElectrumExt for A {
     ) -> Result<(ElectrumUpdate, BTreeMap<K, u32>), Error> {
         let mut request_spks = keychain_spks
             .into_iter()
-            .map(|(k, s)| (k.clone(), s.into_iter()))
+            .map(|(k, s)| (k, s.into_iter()))
             .collect::<BTreeMap<K, _>>();
         let mut scanned_spks = BTreeMap::<(K, u32), (ScriptBuf, bool)>::new();