Refactor foundational temporal types to java.time (#3036)

* Migrates core classes (Clock, Sleeper, TransactionManager) and extensive domain models from Joda-Time to java.time.
* Restores original public API method names while substituting parameters/return values with `java.time.Instant`.
* Updates JAXB XJC `bindings.xjb` to natively generate `java.time.Instant` and `java.time.LocalDate`, eliminating `toDateTime` wrapper methods.
* Fixes XML serializers (`DateAdapter`) to robustly convert OffsetDateTime timezone strings to UTC.
* Cleans up redundant imports and Checkstyle failures across the codebase.

Remaining Joda-Time surface area to migrate in future tasks:
* Command-line parameters (e.g. `DateTimeParameter`, `DateParameter`, `IntervalParameter`) in `google.registry.tools.params`.
* EPP/RDAP flow testing infrastructure (`EppTestCase`, `RdapActionBaseTestCase`, `FlowTestCase`).
* Beam pipelines and Load Testing modules (`Spec11PipelineTest`, `RdePipelineTest`, `RegistryJpaReadTest`, `EppClient`).
* Utility bridges and converters (`DateTimeUtils.toDateTime/toInstant`, `DateTimeConverter`, `UtcDateTimeAdapter`).
* Remaining UI Console tests and Actions.

common/src/main/java/google/registry/util/SystemClock.java

@@ -15,12 +15,10 @@
 package google.registry.util;
 
 import static java.time.temporal.ChronoUnit.MILLIS;
-import static org.joda.time.DateTimeZone.UTC;
 
 import jakarta.inject.Inject;
 import java.time.Instant;
 import javax.annotation.concurrent.ThreadSafe;
-import org.joda.time.DateTime;
 
 /** Clock implementation that proxies to the real system clock. */
 @ThreadSafe
@@ -31,12 +29,6 @@ public class SystemClock implements Clock {
   @Inject
   public SystemClock() {}
 
-  /** Returns the current time. */
-  @Override
-  public DateTime nowUtc() {
-    return DateTime.now(UTC);
-  }
-
   @Override
   public Instant now() {
     // Truncate to milliseconds to match the precision of Joda DateTime and our database schema