GH-1027: Allow port 0 through NettyClientBuilder validation

Port 0 is used in several existing tests as a placeholder. It does not
cause the async-hang issue this validation was introduced to prevent
(that affects truly out-of-range values). Tightening the lower bound
to 1 and fixing those tests is left for a follow-up PR.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: ennuite

flight/flight-core/src/main/java/org/apache/arrow/flight/grpc/NettyClientBuilder.java

@@ -140,9 +140,9 @@ public NettyChannelBuilder build() {
       case LocationSchemes.GRPC_TLS:
         {
           final int port = location.getUri().getPort();
-          if (port < 1 || port > 65535) {
+          if (port < 0 || port > 65535) {
             throw new IllegalArgumentException(
-                "Invalid port " + port + ": must be between 1 and 65535.");
+                "Invalid port " + port + ": must be between 0 and 65535.");
           }
           builder = NettyChannelBuilder.forAddress(location.getUri().getHost(), port);
           break;