fix(telemetry): fix task scheduling order and add test for extended heartbeat default

Move extended heartbeat scheduling after metrics to preserve the
positional task order expected by FakeEventScheduler in tests
(heartbeat=0, metrics=1). Add default value check for
extended_heartbeat_interval in test_configuration.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: khanayan123

src/datadog/telemetry/telemetry_impl.cpp

@@ -223,15 +223,15 @@ void Telemetry::schedule_tasks() {
       config_.heartbeat_interval,
       [this]() { send_payload("app-heartbeat", heartbeat_and_telemetry()); }));
 
-  tasks_.emplace_back(scheduler_->schedule_recurring_event(
-      config_.extended_heartbeat_interval, [this]() {
-        send_payload("app-extended-heartbeat", extended_heartbeat_payload());
-      }));
-
   if (config_.report_metrics) {
     tasks_.emplace_back(scheduler_->schedule_recurring_event(
         config_.metrics_interval, [this]() mutable { capture_metrics(); }));
   }
+
+  tasks_.emplace_back(scheduler_->schedule_recurring_event(
+      config_.extended_heartbeat_interval, [this]() {
+        send_payload("app-extended-heartbeat", extended_heartbeat_payload());
+      }));
 }
 
 Telemetry::~Telemetry() {

test/telemetry/test_configuration.cpp

@@ -21,6 +21,7 @@ TELEMETRY_CONFIGURATION_TEST("defaults") {
   CHECK(cfg->report_metrics == true);
   CHECK(cfg->metrics_interval == 60s);
   CHECK(cfg->heartbeat_interval == 10s);
+  CHECK(cfg->extended_heartbeat_interval == 86400s);
   CHECK(cfg->install_id.has_value() == false);
   CHECK(cfg->install_type.has_value() == false);
   CHECK(cfg->install_time.has_value() == false);