st: fix CI - static-lib object-name collision and missing Transaction defs

Two platform-build failures on this PR, both from Phase 0, both invisible
to the in-tree build and the Linux shared-lib link:

macOS-static / Alpine: the static "withdeps" archive is assembled by
build-support/merge_archives.sh, which extracts every input archive with
`ar -x` into one flat directory. Merging ST_OBJECT_LIB into libpulsar.a
gave it two members named ClientImpl.cc.o (lib/ClientImpl.cc and
lib/st/ClientImpl.cc) and two MessageId.cc.o, so `ar -x` overwrote the
classic objects and libpulsarwithdeps.a lost pulsar::ClientImpl::* and
pulsar::MessageId::* - the example link then failed. Rename the two
colliding st sources to StClientImpl.cc / StMessageId.cc (and the header
to StClientImpl.h) so no two objects in the archive share a basename.
The classes are unchanged; the source GLOB picks the new names up.

Windows: pulsar::st::Transaction::commitAsync()/abortAsync()/state()
were declared and used by the inline commit()/abort() but defined
nowhere. Transaction is PULSAR_PUBLIC (dllexport), so MSVC emits those
inline members and the DLL link needs the out-of-line async defs - a
hard error on Windows, silently tolerated by the mac/Linux .so. Add
lib/st/Transaction.cc with not-implemented-yet stubs (fail with
ResultOperationNotSupported), matching the existing stub pattern; the
real implementation lands in the transaction phase.

Verified on macOS arm64: libpulsar.a has no duplicate members, the real
merge_archives + static example link succeeds, the Transaction symbols
resolve, clang-tidy and clang-format-11 are clean, st tests pass.

Author: merlimat

lib/st/ClientCore.cc

@@ -20,7 +20,7 @@
 
 #include <utility>
 
-#include "ClientImpl.h"
+#include "StClientImpl.h"
 
 namespace pulsar::st::detail {
 

lib/st/PulsarClientBuilder.cc

@@ -24,7 +24,7 @@
 #include <string>
 #include <utility>
 
-#include "ClientImpl.h"
+#include "StClientImpl.h"
 
 namespace pulsar::st {
 

lib/st/ClientImpl.cc lib/st/StClientImpl.cclib/st/ClientImpl.cc renamed to lib/st/StClientImpl.cc

@@ -16,7 +16,7 @@
  * specific language governing permissions and limitations
  * under the License.
  */
-#include "ClientImpl.h"
+#include "StClientImpl.h"
 
 #include <string>
 #include <utility>

lib/st/ClientImpl.h lib/st/StClientImpl.hlib/st/ClientImpl.h renamed to lib/st/StClientImpl.h

@@ -0,0 +1,46 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+#include <pulsar/st/Transaction.h>
+
+namespace pulsar::st {
+
+namespace {
+
+// Transactions are not implemented yet in the scalable-topics client. These
+// out-of-line members still need definitions: Transaction is an exported
+// (PULSAR_PUBLIC) class, so its inline commit()/abort() — which call the async
+// variants — are emitted and must link. They become real in the transaction
+// phase. Until then no live Transaction is handed out (newTransaction fails with
+// ResultOperationNotSupported), so none of these run at runtime.
+Future<void> notImplementedYet() {
+    detail::Promise<void> promise;
+    promise.setError(Error{ResultOperationNotSupported,
+                           "transactions are not implemented yet in the scalable-topics client"});
+    return promise.getFuture();
+}
+
+}  // namespace
+
+TransactionState Transaction::state() const { return TransactionState::Error; }
+
+Future<void> Transaction::commitAsync() const { return notImplementedYet(); }
+
+Future<void> Transaction::abortAsync() const { return notImplementedYet(); }
+
+}  // namespace pulsar::st