[SPARK-52743] Support startRun

### What changes were proposed in this pull request?

This PR aims to support `startRun ` API in order to support `Declarative Pipelines` (SPARK-51727) of Apache Spark `4.1.0-preview1`.

### Why are the changes needed?

To support the new feature incrementally.

### Does this PR introduce _any_ user-facing change?

No, this is a new feature.

### How was this patch tested?

Manually run `Apache Spark 4.1.0-preview1` RC1 .

```
$ sbin/start-connect-server.sh
```

Run the newly added unit test.

<img width="1443" alt="Screenshot 2025-07-09 at 20 20 14" src="https://github.com/user-attachments/assets/4ba9e118-d993-48e2-bdd2-df49d5ddfaca" />

### Was this patch authored or co-authored using generative AI tooling?

No.

Closes #209 from dongjoon-hyun/SPARK-52743.

Authored-by: Dongjoon Hyun <[email protected]>
Signed-off-by: Dongjoon Hyun <[email protected]>

Author: dongjoon-hyun

Sources/SparkConnect/SparkConnectClient.swift

@@ -1214,6 +1214,29 @@ public actor SparkConnectClient {
     }
   }
 
+  @discardableResult
+  func startRun(_ dataflowGraphID: String) async throws -> Bool {
+    try await withGPRC { client in
+      if UUID(uuidString: dataflowGraphID) == nil {
+        throw SparkConnectError.InvalidArgument
+      }
+
+      var startRun = Spark_Connect_PipelineCommand.StartRun()
+      startRun.dataflowGraphID = dataflowGraphID
+
+      var pipelineCommand = Spark_Connect_PipelineCommand()
+      pipelineCommand.commandType = .startRun(startRun)
+
+      var command = Spark_Connect_Command()
+      command.commandType = .pipelineCommand(pipelineCommand)
+
+      let responses = try await execute(self.sessionID!, command)
+      return responses.contains {
+        $0.responseType == .pipelineCommandResult(Spark_Connect_PipelineCommandResult())
+      }
+    }
+  }
+
   private enum URIParams {
     static let PARAM_GRPC_MAX_MESSAGE_SIZE = "grpc_max_message_size"
     static let PARAM_SESSION_ID = "session_id"

Tests/SparkConnectTests/SparkConnectClientTests.swift

@@ -107,4 +107,21 @@ struct SparkConnectClientTests {
     }
     await client.stop()
   }
+
+  @Test
+  func startRun() async throws {
+    let client = SparkConnectClient(remote: TEST_REMOTE)
+    let response = try await client.connect(UUID().uuidString)
+
+    try await #require(throws: SparkConnectError.InvalidArgument) {
+      try await client.startRun("not-a-uuid-format")
+    }
+
+    if response.sparkVersion.version.starts(with: "4.1") {
+      let dataflowGraphID = try await client.createDataflowGraph()
+      #expect(UUID(uuidString: dataflowGraphID) != nil)
+      #expect(try await client.startRun(dataflowGraphID))
+    }
+    await client.stop()
+  }
 }