Migrate EPP Flows, TLD, and Domain Base models to java.time (#3025)

Migrates the massive DomainBase, DomainHistory, and Registrar models to use java.time.Instant natively, removing all deprecated DateTime accessors and fixing their associated JPA converters.
Migrates the Tld entity and its entire JSON/YAML testing ecosystem, including implementing an InstantKeySerializer to preserve millisecond precision in Jackson.
Migrates the entire Epp Flow ecosystem (Create, Update, Delete, Renew, Transfer for Domains/Hosts/Contacts) to use native Instant parameters and operations.
Migrates EppTestCase and EppLifecycleDomainTest to use Instant natively instead of constantly double-wrapping timestamps.
Rebases against upstream and standardizes all Duration and DateTimeUtils static imports across the test suites.

util/src/main/java/google/registry/util/InstantTypeAdapter.java

@@ -14,7 +14,7 @@
 
 package google.registry.util;
 
-import static google.registry.util.DateTimeUtils.ISO_8601_FORMATTER;
+import static google.registry.util.DateTimeUtils.formatInstant;
 
 import com.google.gson.stream.JsonWriter;
 import java.io.IOException;
@@ -41,7 +41,7 @@ public class InstantTypeAdapter extends StringBaseTypeAdapter<Instant> {
     if (value == null) {
       writer.value("null");
     } else {
-      writer.value(ISO_8601_FORMATTER.format(value));
+      writer.value(formatInstant(value));
     }
   }
 }