Bring codebase up to more recent Java standards (#2422)

This includes using the new switch format (though IntelliJ does not yet
understand patterns including default so those aren't used), multiline strings,
replacing some unnecessary type declarations with <>, converting some classes to
records, replacing some Guava predicates with native Java code, and some other
miscellaneous Code Inspection fixes.

proxy/src/test/java/google/registry/proxy/EppProtocolModuleTest.java

@@ -48,10 +48,12 @@ class EppProtocolModuleTest extends ProtocolModuleTest {
   private static final String CLIENT_ADDRESS = "epp.client.tld";
 
   private static final byte[] HELLO_BYTES =
-      ("<?xml version=\"1.0\" encoding=\"UTF-8\" standalone=\"no\"?>\n"
-              + "<epp xmlns=\"urn:ietf:params:xml:ns:epp-1.0\">\n"
-              + "  <hello/>\n"
-              + "</epp>\n")
+      """
+          <?xml version="1.0" encoding="UTF-8" standalone="no"?>
+          <epp xmlns="urn:ietf:params:xml:ns:epp-1.0">
+            <hello/>
+          </epp>
+          """
           .getBytes(UTF_8);
 
   private X509Certificate certificate;

proxy/src/test/java/google/registry/proxy/handler/EppServiceHandlerTest.java

@@ -53,10 +53,12 @@ import org.junit.jupiter.api.Test;
 class EppServiceHandlerTest {
 
   private static final String HELLO =
-      "<?xml version=\"1.0\" encoding=\"UTF-8\" standalone=\"no\"?>\n"
-          + "<epp xmlns=\"urn:ietf:params:xml:ns:epp-1.0\">\n"
-          + "  <hello/>\n"
-          + "</epp>\n";
+      """
+          <?xml version="1.0" encoding="UTF-8" standalone="no"?>
+          <epp xmlns="urn:ietf:params:xml:ns:epp-1.0">
+            <hello/>
+          </epp>
+          """;
 
   private static final String RELAY_HOST = "registry.example.tld";
   private static final String RELAY_PATH = "/epp";