perf(core): Replace Calendar with Date in DateUtils

Avoid constructing Calendar instances when DateUtils only needs the current epoch millis or a Date for an existing millis value. Date stores epoch millis without timezone state, so the returned values are unchanged while avoiding unnecessary Calendar allocation and field computation.

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

Author: adinauer

sentry/src/main/java/io/sentry/Breadcrumb.java

@@ -555,7 +555,7 @@ public Breadcrumb(@Nullable String message) {
     if (timestamp != null) {
       return (Date) timestamp.clone();
     } else if (timestampMs != null) {
-      // we memoize it here into timestamp to avoid instantiating Calendar again and again
+      // we memoize it here into timestamp to avoid creating a Date again and again
       timestamp = DateUtils.getDateTime(timestampMs);
       return timestamp;
     }

sentry/src/main/java/io/sentry/DateUtils.java

@@ -1,13 +1,10 @@
 package io.sentry;
 
-import static io.sentry.vendor.gson.internal.bind.util.ISO8601Utils.TIMEZONE_UTC;
-
 import io.sentry.vendor.gson.internal.bind.util.ISO8601Utils;
 import java.math.BigDecimal;
 import java.math.RoundingMode;
 import java.text.ParseException;
 import java.text.ParsePosition;
-import java.util.Calendar;
 import java.util.Date;
 import org.jetbrains.annotations.ApiStatus;
 import org.jetbrains.annotations.NotNull;
@@ -24,10 +21,9 @@ private DateUtils() {}
    *
    * @return the UTC Date
    */
-  @SuppressWarnings("JdkObsolete")
+  @SuppressWarnings("JavaUtilDate")
   public static @NotNull Date getCurrentDateTime() {
-    final Calendar calendar = Calendar.getInstance(TIMEZONE_UTC);
-    return calendar.getTime();
+    return new Date();
   }
 
   /**
@@ -78,10 +74,9 @@ private DateUtils() {}
    * @param millis the UTC millis from the epoch
    * @return the UTC Date
    */
+  @SuppressWarnings("JavaUtilDate")
   public static @NotNull Date getDateTime(final long millis) {
-    final Calendar calendar = Calendar.getInstance(TIMEZONE_UTC);
-    calendar.setTimeInMillis(millis);
-    return calendar.getTime();
+    return new Date(millis);
   }
 
   /**

sentry/src/test/java/io/sentry/DateUtilsTest.kt

@@ -86,6 +86,7 @@ class DateUtilsTest {
     val utcActual = convertDate(actual)
     val timestamp = utcActual.format(isoFormat)
 
+    assertEquals(millis, actual.time)
     assertEquals("2020-06-07T12:38:12.631Z", timestamp)
   }