feat: add engineVersion option to projection create

Exposes the V2 projection engine introduced in KurrentDB. Setting
engineVersion(2) on CreateProjectionOptions selects V2; 0 (default)
or 1 selects V1. The option is pinned at create time and cannot be
changed via update.

Author: w1am

src/main/java/io/kurrent/dbclient/CreateProjection.java

@@ -12,6 +12,7 @@ class CreateProjection {
     private final String query;
     private final boolean trackEmittedStreams;
     private final boolean emitEnabled;
+    private final int engineVersion;
     private final CreateProjectionOptions options;
 
     public CreateProjection(final GrpcClient client, final String projectionName, final String query,
@@ -22,6 +23,7 @@ public CreateProjection(final GrpcClient client, final String projectionName, fi
         this.query = query;
         this.trackEmittedStreams = options.isTrackingEmittedStreams();
         this.emitEnabled = options.isEmitEnabled();
+        this.engineVersion = options.getEngineVersion();
         this.options = options;
     }
 
@@ -36,6 +38,7 @@ public CompletableFuture execute() {
             Projectionmanagement.CreateReq.Options.Builder optionsBuilder =
                 Projectionmanagement.CreateReq.Options.newBuilder()
                     .setQuery(query)
+                    .setEngineVersion(engineVersion)
                     .setContinuous(continuousBuilder);
 
             Projectionmanagement.CreateReq request = Projectionmanagement.CreateReq.newBuilder()

src/main/java/io/kurrent/dbclient/CreateProjectionOptions.java

@@ -6,6 +6,7 @@
 public class CreateProjectionOptions extends OptionsBase<CreateProjectionOptions> {
     private boolean trackEmittedStreams;
     private boolean emitEnabled;
+    private int engineVersion;
 
     private CreateProjectionOptions() {
         this.trackEmittedStreams = false;
@@ -26,6 +27,10 @@ boolean isEmitEnabled() {
         return emitEnabled;
     }
 
+    int getEngineVersion() {
+        return engineVersion;
+    }
+
     /**
      * If true, the projection tracks all streams it creates.
      */
@@ -41,4 +46,17 @@ public CreateProjectionOptions emitEnabled(boolean value) {
         this.emitEnabled = value;
         return this;
     }
+
+    /**
+     * Selects the projection engine version. {@code 0} (default) or {@code 1} selects V1;
+     * {@code 2} selects the V2 engine, which provides partition-based parallel processing.
+     * <p>
+     * The engine version is pinned at create time and cannot be changed via update.
+     * V2 has limitations versus V1 — notably, {@code trackEmittedStreams} is rejected,
+     * result streams are not emitted, and bi-state projections are not supported.
+     */
+    public CreateProjectionOptions engineVersion(int value) {
+        this.engineVersion = value;
+        return this;
+    }
 }

src/main/proto/kurrentdb/protocol/v1/projectionmanagement.proto

@@ -28,6 +28,7 @@ message CreateReq {
 			Continuous continuous = 3;
 		}
 		string query = 4;
+		int32 engine_version = 5; // 0 or 1 = v1 (default), 2 = v2
 
 		message Transient {
 			string name = 1;