[SPARK-52524] Support Timestamp type

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

This PR aims to support `Timestamp` type in `Row` and `DataFrame.collect`.

### Why are the changes needed?

Previously, `Timestamp` is supported inside `Spark Connect Server`-side operation only, e.g. `DataFrame.show`.

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

No, this is an additional type.

### How was this patch tested?

Pass the CIs.

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

No.

Closes #202 from dongjoon-hyun/SPARK-52524.

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

Author: dongjoon-hyun

Sources/SparkConnect/DataFrame.swift

@@ -429,6 +429,22 @@ public actor DataFrame: Sendable {
               values.append(array.asAny(i) as? Decimal)
             case .primitiveInfo(.date32):
               values.append(array.asAny(i) as! Date)
+            case .timeInfo(.timestamp):
+              let timestampType = column.data.type as! ArrowTypeTimestamp
+              assert(timestampType.timezone == "Etc/UTC")
+              let timestamp = array.asAny(i) as! Int64
+              let timeInterval =
+                switch timestampType.unit {
+                case .seconds:
+                  TimeInterval(timestamp)
+                case .milliseconds:
+                  TimeInterval(timestamp) / 1_000
+                case .microseconds:
+                  TimeInterval(timestamp) / 1_000_000
+                case .nanoseconds:
+                  TimeInterval(timestamp) / 1_000_000_000
+                }
+              values.append(Date(timeIntervalSince1970: timeInterval))
             case ArrowType.ArrowBinary:
               values.append((array as! AsString).asString(i).utf8)
             case .complexInfo(.strct):

Sources/SparkConnect/Row.swift

@@ -71,6 +71,8 @@ public struct Row: Sendable, Equatable {
         return a == b
       } else if let a = x as? Decimal, let b = y as? Decimal {
         return a == b
+      } else if let a = x as? Date, let b = y as? Date {
+        return a == b
       } else if let a = x as? String, let b = y as? String {
         return a == b
       } else {

Tests/SparkConnectTests/DataFrameTests.swift

@@ -932,6 +932,19 @@ struct DataFrameTests {
       #expect(try await df.collect() == expected)
       await spark.stop()
     }
+
+    @Test
+    func timestamp() async throws {
+      let spark = try await SparkSession.builder.getOrCreate()
+      let df = try await spark.sql(
+        "SELECT TIMESTAMP '2025-05-01 16:23:40', TIMESTAMP '2025-05-01 16:23:40.123456'")
+      let expected = [
+        Row(
+          Date(timeIntervalSince1970: 1746116620.0), Date(timeIntervalSince1970: 1746116620.123456))
+      ]
+      #expect(try await df.collect() == expected)
+      await spark.stop()
+    }
   #endif
 
   @Test