feat: make volatile session (#330)

Author: KirillKurdyukov

topic/src/main/java/tech/ydb/topic/read/impl/ReaderImpl.java

@@ -43,7 +43,7 @@ public abstract class ReaderImpl extends GrpcStreamRetrier {
 
     private static final int DEFAULT_DECOMPRESSION_THREAD_COUNT = 4;
 
-    private ReadSessionImpl session;
+    private volatile ReadSessionImpl session;
     private final ReaderSettings settings;
     private final TopicRpc topicRpc;
     private final Executor decompressionExecutor;

topic/src/main/java/tech/ydb/topic/write/impl/WriterImpl.java

@@ -37,7 +37,7 @@
 public abstract class WriterImpl extends GrpcStreamRetrier {
     private static final Logger logger = LoggerFactory.getLogger(WriterImpl.class);
 
-    private WriteSessionImpl session;
+    private volatile WriteSessionImpl session;
     private final WriterSettings settings;
     private final TopicRpc topicRpc;
     private final AtomicReference<CompletableFuture<InitResult>> initResultFutureRef = new AtomicReference<>(null);