Migrate dd-trace-core groovy files to java part 5 (#11217)

Migrate dd-trace-core groovy files to java part 5

we migrate 4 tests:
 - DDSpanContextTest
 - DDSpanSerializationTest
 - DDSpanTest
 - KnuthSamplingRateTest

# Conflicts:
#	dd-trace-core/src/test/groovy/datadog/trace/core/DDSpanContextTest.groovy
#	dd-trace-core/src/test/groovy/datadog/trace/core/DDSpanTest.groovy
#	dd-trace-core/src/test/groovy/datadog/trace/core/KnuthSamplingRateTest.groovy

address comments

address comments

resolve conflicts

Co-authored-by: devflow.devflow-routing-intake <devflow.devflow-routing-intake@kubernetes.us1.ddbuild.io>

Author: jpbempel

.claude/skills/migrate-groovy-to-java/SKILL.md

@@ -30,6 +30,8 @@ When converting Groovy code to Java code, make sure that:
 - Do not mark local variables `final`
 - Ensure variables are human-readable; avoid single-letter names and pre-define variables that are referenced multiple times
 - When translating Spock `Mock(...)` usage, use `libs.bundles.mockito` instead of writing manual recording/stub implementations
+- Keep inline comments
+- Migrate the named Spock clauses if they exist as inline comments in the Java unit test
 
 TableTest usage
   Import: `import org.tabletest.junit.TableTest;`

dd-trace-core/src/main/java/datadog/trace/common/writer/ddagent/TraceMapperV0_5.java

@@ -125,6 +125,16 @@ public String endpoint() {
     return "v0.5";
   }
 
+  // Visible for tests
+  Map<Object, Integer> getEncoding() {
+    return encoding;
+  }
+
+  // Visible for tests
+  GrowableBuffer getDictionary() {
+    return dictionary;
+  }
+
   private static class DictionaryMapper implements Mapper<Object> {
 
     @Override

dd-trace-core/src/main/java/datadog/trace/core/PendingTrace.java

@@ -233,6 +233,11 @@ void setLongRunningTrackedState(int state) {
     LONG_RUNNING_STATE.set(this, state);
   }
 
+  // @VisibleForTesting
+  int getPendingReferenceCount() {
+    return pendingReferenceCount;
+  }
+
   boolean empty() {
     return 0 >= COMPLETED_SPAN_COUNT.get(this) + PENDING_REFERENCE_COUNT.get(this);
   }