Add src/wallet/* code to wallet:: namespace

src/wallet/external_signer_scriptpubkeyman.cpp

@@ -13,6 +13,7 @@
 #include <utility>
 #include <vector>
 
+namespace wallet {
 bool ExternalSignerScriptPubKeyMan::SetupDescriptor(std::unique_ptr<Descriptor> desc)
 {
     LOCK(cs_desc_man);
@@ -82,3 +83,4 @@ TransactionError ExternalSignerScriptPubKeyMan::FillPSBT(PartiallySignedTransact
     if (finalize) FinalizePSBT(psbt); // This won't work in a multisig setup
     return TransactionError::OK;
 }
+} // namespace wallet