[SPARK-54550][CONNECT] Handle ConnectException gracefully in SparkConnectStatement.close()

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

This PR fixes two issues in `org.apache.spark.sql.connect.client.jdbc.SparkConnectStatement.close()`:
- Added `try-catch` to silently handle `ConnectException` during `interruptOperation()` when the server is unavailable
- Fixed bug: changed closed = false to closed = true at the end of the method

### Why are the changes needed?

- ConnectException handling: The `SparkConnectStatement.close()` method should not throw exceptions during cleanup. Connection exceptions during cleanup are not actionable and only mask more important exceptions.
- closed flag bug: Setting closed = false is incorrect and could allow reuse of closed statements.

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

No

### How was this patch tested?

Existing unit tests pass

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

No

Closes #53260 from vinodkc/br_handle_close_exception.

Authored-by: vinodkc <[email protected]>
Signed-off-by: Dongjoon Hyun <[email protected]>
(cherry picked from commit bb36695)
Signed-off-by: Dongjoon Hyun <[email protected]>

Author: vinodkc

sql/connect/client/jdbc/src/main/scala/org/apache/spark/sql/connect/client/jdbc/SparkConnectStatement.scala

@@ -35,14 +35,21 @@ class SparkConnectStatement(conn: SparkConnectConnection) extends Statement {
   override def close(): Unit = synchronized {
     if (!closed) {
       if (operationId != null) {
-        conn.spark.interruptOperation(operationId)
+        try {
+          conn.spark.interruptOperation(operationId)
+        } catch {
+          case _: java.net.ConnectException =>
+            // Ignore ConnectExceptions during cleanup as the operation may have already completed
+            // or the server may be unavailable. The important part is marking this statement
+            // as closed to prevent further use.
+        }
         operationId = null
       }
       if (resultSet != null) {
         resultSet.close()
         resultSet = null
       }
-      closed = false
+      closed = true
     }
   }