[SPARK-56229] Remove io.netty.noUnsafe from default JVM args according to Netty change

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

This PR removes `-Dio.netty.noUnsafe=true` from the default JVM args in `values.yaml`.

### Why are the changes needed?

Netty 4.2.2+ have a correct implementation instead of `Unsafe` usage for Java 25+ like the following instead of the legacy `Unsafe` operation.

- netty/netty#15231
- netty/netty#15338

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

No.

### How was this patch tested?

Pass the CIs with the existing tests.

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

Generated-by: Claude Code (claude-4-opus)

Closes #593 from dongjoon-hyun/SPARK-56229.

Authored-by: Dongjoon Hyun <dongjoon@apache.org>
Signed-off-by: Dongjoon Hyun <dongjoon@apache.org>

Author: dongjoon-hyun

build-tools/helm/spark-kubernetes-operator/values.yaml

@@ -41,7 +41,7 @@ operatorDeployment:
     # https://kubernetes.io/docs/concepts/scheduling-eviction/topology-spread-constraints/
     topologySpreadConstraints: [ ]
     operatorContainer:
-      jvmArgs: "-Dfile.encoding=UTF8 -XX:+ExitOnOutOfMemoryError -XX:+UseParallelGC -XX:InitialRAMPercentage=80 -XX:MaxRAMPercentage=80 -XX:+AlwaysPreTouch -Dio.netty.noUnsafe=true -XX:+UseCompactObjectHeaders"
+      jvmArgs: "-Dfile.encoding=UTF8 -XX:+ExitOnOutOfMemoryError -XX:+UseParallelGC -XX:InitialRAMPercentage=80 -XX:MaxRAMPercentage=80 -XX:+AlwaysPreTouch -XX:+UseCompactObjectHeaders"
       env:
         - name: "SPARK_USER"
           value: "spark"