Make GrpcStubs channel closeable by calling bot

Each bot has its own gRPC channel and set of service stubs,
and a single bot's channel & stubs last the bot's lifetime.
However, RegtestTradePaymentSimulator instance is a bot too, with it's
own channel & stubs, which should be closed at the end of each run().

java-examples/src/main/java/bisq/bots/GrpcStubs.java

@@ -19,6 +19,7 @@ package bisq.bots;
 
 import bisq.proto.grpc.*;
 import io.grpc.CallCredentials;
+import io.grpc.ManagedChannel;
 import io.grpc.ManagedChannelBuilder;
 import lombok.extern.slf4j.Slf4j;
 
@@ -40,19 +41,13 @@ final class GrpcStubs {
     public final TradesGrpc.TradesBlockingStub tradesService;
     public final WalletsGrpc.WalletsBlockingStub walletsService;
 
+    private final ManagedChannel channel;
+
     public GrpcStubs(String apiHost, int apiPort, String apiPassword) {
         CallCredentials credentials = new PasswordCallCredentials(apiPassword);
 
-        var channel = ManagedChannelBuilder.forAddress(apiHost, apiPort).usePlaintext().build();
+        this.channel = ManagedChannelBuilder.forAddress(apiHost, apiPort).usePlaintext().build();
-        Runtime.getRuntime().addShutdownHook(new Thread(() -> {
+        Runtime.getRuntime().addShutdownHook(new Thread(this::close));
-            try {
-                log.info("Shutting down bot's grpc channel.");
-                channel.shutdown().awaitTermination(1, SECONDS);
-                log.info("Bot channel shutdown complete.");
-            } catch (InterruptedException ex) {
-                throw new IllegalStateException(ex);
-            }
-        }));
 
         this.disputeAgentsService = DisputeAgentsGrpc.newBlockingStub(channel).withCallCredentials(credentials);
         this.helpService = HelpGrpc.newBlockingStub(channel).withCallCredentials(credentials);
@@ -64,4 +59,16 @@ final class GrpcStubs {
         this.tradesService = TradesGrpc.newBlockingStub(channel).withCallCredentials(credentials);
         this.walletsService = WalletsGrpc.newBlockingStub(channel).withCallCredentials(credentials);
     }
+
+    public void close() {
+        try {
+            if (!channel.isShutdown()) {
+                log.info("Shutting down bot's grpc channel.");
+                channel.shutdown().awaitTermination(1, SECONDS);
+                log.info("Bot channel shutdown complete.");
+            }
+        } catch (InterruptedException ex) {
+            throw new IllegalStateException(ex);
+        }
+    }
 }

java-examples/src/main/java/bisq/bots/RegtestTradePaymentSimulator.java

@@ -116,6 +116,8 @@ public class RegtestTradePaymentSimulator extends AbstractBot {
         sleep(pollingInterval);
         log.info("Trade is completed, printing all closed trades and exiting {}.", this.getClass().getSimpleName());
         printTradesSummary(CLOSED);
+        log.info("Closing {}'s gRPC channel.", this.getClass().getSimpleName());
+        super.grpcStubs.close();
     }
 
     private void waitForTakerDepositTxConfirmation() {