[SPARK-50870][SQL] Add the timezone when casting to timestamp in V2ScanRelationPushDown

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

Add the timezone information to a cast expression when the destination type requires it.

### Why are the changes needed?

When current_timestamp() is materialized as a string, the timezone information is gone (e.g., 2024-12-27 10:26:27.684158) which prohibits further optimization rules from being applied to the affected data source.

For example,

```
Project [1735900357973433#10 AS current_timestamp()#6]
+- 'Project [cast(2025-01-03 10:32:37.973433#11 as timestamp) AS 1735900357973433#10]
   +- RelationV2[2025-01-03 10:32:37.973433#11] xxx
```

-> This query fails to execute because the injected cast expression lacks the timezone information.

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

No.

### How was this patch tested?

Existing tests.

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

No.

Closes apache#49549 from changgyoopark-db/SPARK-50870.

Authored-by: changgyoopark-db <changgyoo.park@databricks.com>
Signed-off-by: Wenchen Fan <wenchen@databricks.com>

Author: changgyoopark-db

sql/core/src/main/scala/org/apache/spark/sql/execution/datasources/v2/V2ScanRelationPushDown.scala

@@ -328,7 +328,12 @@ object V2ScanRelationPushDown extends Rule[LogicalPlan] with PredicateHelper {
     if (expression.dataType == expectedDataType) {
       expression
     } else {
-      Cast(expression, expectedDataType)
+      val cast = Cast(expression, expectedDataType)
+      if (cast.timeZoneId.isEmpty && cast.needsTimeZone) {
+        cast.withTimeZone(conf.sessionLocalTimeZone)
+      } else {
+        cast
+      }
     }
 
   def buildScanWithPushedAggregate(plan: LogicalPlan): LogicalPlan = plan.transform {