CNDB-12272: Fix SimpleClientPerfTest (#1477)

### What is the issue
SimpleClientPerfTest has been failing in CI since changes from
CNDB-10759

### What does this PR fix and why was it fixed
This change in `SimpleClientPerfTest`, updates the anonymous class
`Message.Codec<QueryMessage>` to override the correct method, `public
CompletableFuture<Response> maybeExecuteAsync` from `QueryMessage`,
whose signature was changed as part of CNDB-10759.

### Checklist before you submit for review
- [ ] Make sure there is a PR in the CNDB project updating the Converged
Cassandra version
- [ ] Use `NoSpamLogger` for log lines that may appear frequently in the
logs
- [ ] Verify test results on Butler
- [ ] Test coverage for new/modified code is > 80%
- [ ] Proper code formatting
- [ ] Proper title for each commit staring with the project-issue
number, like CNDB-1234
- [ ] Each commit has a meaningful description
- [ ] Each commit is not very long and contains related changes
- [ ] Renames, moves and reformatting are in distinct commits

Author: djatnieks

test/burn/org/apache/cassandra/transport/SimpleClientBurnTest.java

@@ -113,11 +113,12 @@ public QueryMessage decode(ByteBuf body, ProtocolVersion version)
                 QueryMessage queryMessage = QueryMessage.codec.decode(body, version);
                 return new QueryMessage(queryMessage.query, queryMessage.options)
                 {
-                    public Message.Response executeSync(QueryState state, long queryStartNanoTime, boolean traceRequest)
+                    @Override
+                    public CompletableFuture<Response> maybeExecuteAsync(QueryState state, long queryStartNanoTime, boolean traceRequest)
                     {
                         int idx = Integer.parseInt(queryMessage.query);
                         SizeCaps caps = idx % largeMessageFrequency == 0 ? largeMessageCap : smallMessageCap;
-                        return generateRows(idx, caps);
+                        return CompletableFuture.completedFuture(generateRows(idx, caps));
                     }
                 };
             }

test/burn/org/apache/cassandra/transport/SimpleClientPerfTest.java

@@ -172,10 +172,11 @@ public QueryMessage decode(ByteBuf body, ProtocolVersion version)
                 QueryMessage queryMessage = QueryMessage.codec.decode(body, version);
                 return new QueryMessage(queryMessage.query, queryMessage.options)
                 {
-                    public Message.Response executeSync(QueryState state, long queryStartNanoTime, boolean traceRequest)
+                    @Override
+                    public CompletableFuture<Response> maybeExecuteAsync(QueryState state, long queryStartNanoTime, boolean traceRequest)
                     {
                         int idx = Integer.parseInt(queryMessage.query); // unused
-                        return generateRows(idx, responseCaps);
+                        return CompletableFuture.completedFuture(generateRows(idx, responseCaps));
                     }
                 };
             }