chore: Cap gRPC inbound message size at ~2 GiB and metadata at 16 MiB

Extract named constants MAX_INBOUND_MESSAGE_SIZE (Integer.MAX_VALUE ≈ 2 GiB)
and MAX_INBOUND_METADATA_SIZE (16 MiB) to make the caps explicit and prevent
unbounded metadata from consuming heap on large dataset transfers.

Author: lukekim

src/main/java/ai/spice/SpiceClient.java

@@ -133,9 +133,14 @@ public class SpiceClient implements AutoCloseable {
     // Cached Gson instance for JSON serialization (thread-safe)
     private static final Gson GSON = new Gson();
 
+    // 2 GiB cap for large dataset results (max safe signed-int value)
+    private static final int MAX_INBOUND_MESSAGE_SIZE = Integer.MAX_VALUE;
+    // 16 MiB cap for gRPC metadata/headers
+    private static final int MAX_INBOUND_METADATA_SIZE = 16 * 1024 * 1024;
+
     // Cached HttpClient for refresh operations (thread-safe, connection pooling)
     private static final HttpClient HTTP_CLIENT = HttpClient.newBuilder()
-            .connectTimeout(Duration.ofSeconds(10))
+            .connectTimeout(Duration.ofSeconds(15))
             .build();
 
     // Pre-computed parameter field names to avoid string concatenation in hot path
@@ -274,8 +279,8 @@ private synchronized void buildFlightClient() {
                 .keepAliveTime(30, java.util.concurrent.TimeUnit.SECONDS)
                 .keepAliveTimeout(10, java.util.concurrent.TimeUnit.SECONDS)
                 .keepAliveWithoutCalls(true)
-                .maxInboundMessageSize(Integer.MAX_VALUE)
-                .maxInboundMetadataSize(Integer.MAX_VALUE);
+                .maxInboundMessageSize(MAX_INBOUND_MESSAGE_SIZE)
+                .maxInboundMetadataSize(MAX_INBOUND_METADATA_SIZE);
         ManagedChannel channel = channelBuilder.build();
 
         try {