Replace SimpleDateFormat with java.time.Instant for timestamp parsing

Instant.parse() handles all ISO 8601 formats natively, avoids
deprecated SimpleDateFormat, and throws DateTimeParseException
with clear context on invalid input instead of returning null.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: MichaelGHSeg

e2e-cli/src/main/kotlin/cli/Main.kt

@@ -5,10 +5,8 @@ import com.google.gson.reflect.TypeToken
 import com.segment.analytics.Analytics
 import com.segment.analytics.Callback
 import com.segment.analytics.messages.*
-import java.text.SimpleDateFormat
+import java.time.Instant
 import java.util.Date
-import java.util.Locale
-import java.util.TimeZone
 import java.util.concurrent.CountDownLatch
 import java.util.concurrent.TimeUnit
 import java.util.concurrent.atomic.AtomicBoolean
@@ -187,14 +185,5 @@ fun sendEvent(analytics: Analytics, event: Map<String, Any>) {
 }
 
 private fun parseTimestamp(iso: String): Date {
-    val format = SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ss.SSS'Z'", Locale.US)
-    format.timeZone = TimeZone.getTimeZone("UTC")
-    return try {
-        format.parse(iso)!!
-    } catch (_: Exception) {
-        // Fallback: try without millis
-        val fallback = SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ss'Z'", Locale.US)
-        fallback.timeZone = TimeZone.getTimeZone("UTC")
-        fallback.parse(iso)!!
-    }
+    return Date.from(Instant.parse(iso))
 }