fix: add _dd.p.ksr to expected meta maps in DDAgentApiTest

The ksr implementation now adds _dd.p.ksr tag to spans with agent
sampling rate, so the msgpack serialization test expectations need
to include it.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: bm1549

dd-trace-core/src/test/groovy/datadog/trace/common/writer/DDAgentApiTest.groovy

@@ -164,7 +164,7 @@ class DDAgentApiTest extends DDCoreSpecification {
     [[buildSpan(1L, "service.name", "my-service", PropagationTags.factory().fromHeaderValue(PropagationTags.HeaderType.DATADOG, "_dd.p.usr=123"))]] | [[new TreeMap<>([
       "duration" : 10,
       "error"    : 0,
-      "meta"     : ["thread.name": Thread.currentThread().getName(), "_dd.p.usr": "123", "_dd.p.dm": "-1", "_dd.svc_src" : "m"] +
+      "meta"     : ["thread.name": Thread.currentThread().getName(), "_dd.p.usr": "123", "_dd.p.dm": "-1", "_dd.p.ksr": "1", "_dd.svc_src" : "m"] +
         (Config.get().isExperimentalPropagateProcessTagsEnabled() ? ["_dd.tags.process" : ProcessTags.getTagsForSerialization().toString()] : []),
       "metrics"  : [
         (DDSpanContext.PRIORITY_SAMPLING_KEY)          : 1,
@@ -185,7 +185,7 @@ class DDAgentApiTest extends DDCoreSpecification {
     [[buildSpan(100L, "resource.name", "my-resource", PropagationTags.factory().fromHeaderValue(PropagationTags.HeaderType.DATADOG, "_dd.p.usr=123"))]] | [[new TreeMap<>([
       "duration" : 10,
       "error"    : 0,
-      "meta"     : ["thread.name": Thread.currentThread().getName(), "_dd.p.usr": "123", "_dd.p.dm": "-1"] +
+      "meta"     : ["thread.name": Thread.currentThread().getName(), "_dd.p.usr": "123", "_dd.p.dm": "-1", "_dd.p.ksr": "1"] +
         (Config.get().isExperimentalPropagateProcessTagsEnabled() ? ["_dd.tags.process" : ProcessTags.getTagsForSerialization().toString()] : []),
       "metrics"  : [
         (DDSpanContext.PRIORITY_SAMPLING_KEY)          : 1,