Complete Joda-Time to java.time migration (#3039)

This completes the exhaustive refactoring of foundational temporal types from Joda-Time to the native java.time API across the entire codebase.

- Replaced org.joda.time.DateTime, Instant, LocalDate, and Duration with java.time equivalents.
- Audited and updated Clock implementations (FakeClock, SystemClock). Added nowMillis(), nowDate(), and nowDateTime() to eliminate repetitive conversions and maintain parallel naming.
- Replaced ZonedDateTime with OffsetDateTime globally per go/avoid-zdt. OffsetDateTime is a better fit as we use a hardcoded ZoneOffset.UTC throughout the system, making geographical time zone rules (like daylight saving time) irrelevant and preventing serialization ambiguities. Added a presubmit check.
- Completely removed all transitional bridge methods from DateTimeUtils and deleted obsolete converters (e.g., DateTimeConverter).
- Updated testing infrastructure, Apache Beam pipelines, custom JCommander parameters, and networking modules to solely rely on java.time primitives.
- Retained the lone necessary org.joda.time.Instant usage in SafeBrowsingTransforms required by the Apache Beam API.
- Cleared Gradle lockfiles and removed the joda-time dependency entirely from the build configuration.

load-testing/gradle.lockfile

@@ -40,7 +40,6 @@ io.netty:netty-resolver:4.1.133.Final=compileClasspath,deploy_jar,runtimeClasspa
 io.netty:netty-transport-native-unix-common:4.1.133.Final=compileClasspath,deploy_jar,runtimeClasspath,testCompileClasspath,testRuntimeClasspath
 io.netty:netty-transport:4.1.133.Final=compileClasspath,deploy_jar,runtimeClasspath,testCompileClasspath,testRuntimeClasspath
 javax.inject:javax.inject:1=annotationProcessor,testAnnotationProcessor
-joda-time:joda-time:2.14.2=compileClasspath,deploy_jar,runtimeClasspath,testCompileClasspath,testRuntimeClasspath
 net.sf.saxon:Saxon-HE:12.5=checkstyle
 org.antlr:antlr4-runtime:4.13.2=checkstyle
 org.apache.commons:commons-lang3:3.8.1=checkstyle