wip: use spk cache when signing

if the wallet has a large amount of SPKMans (e.g. after migrating a legacy wallet), we can
avoid iterating through all of them by using the spk cache. The downside is we iterate through the tx inputs
again when trying to sign with a particular SPK. If all our inputs are managed by the same SPK, then
this is always faster due to the early exit. If not, its still faster when number of inputs < SPKMans in the wallet.
It is slower in the case where number of inputs > SPKMans and all of the inputs are from different SPKs, which
seems unlikely. This worst case could be improved by threading the input all the way through when signing, but
that needs more thought.

src/wallet/wallet.cpp

@@ -2121,11 +2121,14 @@ bool CWallet::SignTransaction(CMutableTransaction& tx) const
 bool CWallet::SignTransaction(CMutableTransaction& tx, const std::map<COutPoint, Coin>& coins, int sighash, std::map<int, bilingual_str>& input_errors) const
 {
     // Try to sign with all ScriptPubKeyMans
-    for (ScriptPubKeyMan* spk_man : GetAllScriptPubKeyMans()) {
-        // spk_man->SignTransaction will return true if the transaction is complete,
-        // so we can exit early and return true if that happens
-        if (spk_man->SignTransaction(tx, coins, sighash, input_errors)) {
-            return true;
+    for (const CTxIn& tx_in : tx.vin) {
+        // Use the scriptPubKey cache to grab the correct set of SPKMan(s)
+        for (const ScriptPubKeyMan* spk_man : GetScriptPubKeyMans(coins.at(tx_in.prevout).out.scriptPubKey)) {
+            // spk_man->SignTransaction will return true if the transaction is complete,
+            // so we can exit early and return true if that happens
+            if (spk_man->SignTransaction(tx, coins, sighash, input_errors)) {
+                return true;
+            }
         }
     }