[wallet] Verify unconfirmed transactions after syncing

Verify the unconfirmed transactions we download against the consensus
rules. This is currently exposed as an extra `verify` feature, since it
depends on a pre-release version of `bitcoinconsensus`.

Closes #352

.github/workflows/cont_integration.yml

@@ -23,6 +23,7 @@ jobs:
           - esplora,key-value-db,electrum
           - compiler
           - rpc
+          - verify
     steps:
       - name: checkout
         uses: actions/checkout@v2