Migrate dd-trace-core groovy files to java part 1

Migrate dd-trace-api module from Groovy to Java, using the
/migrate-groovy-to-java Claude skill. This is part 1 with five file
changes with no dependencies.

Author: jpbempel

dd-trace-core/build.gradle

@@ -96,6 +96,7 @@ dependencies {
   testCompileOnly libs.autoservice.annotation
 
   testImplementation project(':dd-java-agent:testing')
+  testImplementation libs.bundles.mockito
   testImplementation project(path: ':dd-java-agent:agent-otel:otel-bootstrap', configuration: 'shadow')
   testImplementation project(':remote-config:remote-config-core')
   testImplementation project(':products:metrics:metrics-lib')