chore: assert sessionSyncContext on all stream-callback handlers

Five SessionImpl handlers reachable from dispatchResponseMessage —
handleSessionParamsResponse, handleSessionRefreshConfigResponse,
handleGoAwayResponse, handleUnknownResponseMessage — and the
dispatchStreamClosed entry point were missing the
throwIfNotInThisSynchronizationContext assertion that the other handlers
already have. The assertions are strictly redundant today (every caller
is either dispatchResponseMessage, which already asserts, or
sessionSyncContext.execute), but the asymmetry is incidental and adding
them uniformly documents the threading contract and guards against
future direct callers.

Author: igorbernstein2

java-bigtable/google-cloud-bigtable/src/main/java/com/google/cloud/bigtable/data/v2/internal/session/SessionImpl.java

@@ -538,6 +538,7 @@ private void handleOpenSessionResponse(OpenSessionResponse openSession) {
   }
 
   private void handleSessionParamsResponse(SessionParametersResponse resp) {
+    sessionSyncContext.throwIfNotInThisSynchronizationContext();
     if (state.phase >= SessionState.CLOSING.phase) {
       logger.fine(String.format("Stream was already %s when session params were received", state));
       return;
@@ -615,6 +616,7 @@ private void handleHeartBeatResponse(HeartbeatResponse ignored) {
   }
 
   private void handleSessionRefreshConfigResponse(SessionRefreshConfig config) {
+    sessionSyncContext.throwIfNotInThisSynchronizationContext();
     Metadata grpcMetadata = new Metadata();
     config
         .getMetadataList()
@@ -679,6 +681,7 @@ private void handleVRpcErrorResponse(ErrorResponse error) {
   }
 
   private void handleGoAwayResponse(GoAwayResponse goAwayResponse) {
+    sessionSyncContext.throwIfNotInThisSynchronizationContext();
     if (state.phase >= SessionState.CLOSING.phase) {
       debugTagTracer.record(TelemetryConfiguration.Level.WARN, "session_go_away_ignored");
       logger.warning(
@@ -707,11 +710,13 @@ private void handleGoAwayResponse(GoAwayResponse goAwayResponse) {
   }
 
   private void handleUnknownResponseMessage(SessionResponse message) {
+    sessionSyncContext.throwIfNotInThisSynchronizationContext();
     debugTagTracer.record(TelemetryConfiguration.Level.WARN, "session_unknown_response");
     logger.warning(String.format("%s Unknown control message: %s", info.getLogName(), message));
   }
 
   private void dispatchStreamClosed(Status status, Metadata trailers) {
+    sessionSyncContext.throwIfNotInThisSynchronizationContext();
     SessionState prevState = state;
 
     if (!status.isOk()) {