[SPARK-54551][CONNECT][TESTS] Fix random hangs in SparkConnectJdbcDataTypeSuite

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

Added explicit stdout/stderr redirection to Redirect.DISCARD for the child Spark Connect server process in non-debug mode in SparkConnectServerUtils.

### Why are the changes needed?

SparkConnectJdbcDataTypeSuite randomly hangs because the child server process blocks on write() calls when stdout/stderr pipe buffers fill up. Without consuming the output, the buffers reach capacity and cause the process to block indefinitely.

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

No.

### How was this patch tested?

Manually tested verified `SparkConnectJdbcDataTypeSuite` no longer randomly hangs and all tests pass consistently.

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

No

Closes #53261 from vinodkc/br_handle_std_pipe.

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

Author: vinodkc

sql/connect/client/jvm/src/test/scala/org/apache/spark/sql/connect/test/RemoteSparkSession.scala

@@ -93,6 +93,11 @@ object SparkConnectServerUtils {
     if (isDebug) {
       builder.redirectError(Redirect.INHERIT)
       builder.redirectOutput(Redirect.INHERIT)
+    } else {
+      // If output is not consumed, the stdout/stderr pipe buffers will fill up,
+      // causing the server process to block on write() calls
+      builder.redirectError(Redirect.DISCARD)
+      builder.redirectOutput(Redirect.DISCARD)
     }
 
     val process = builder.start()