Cover native Go Dags in the go_sdk e2e test

[jason810496]

• Depends on Parse native Go Dags and show each Dag's own source #74341 and Go SDK: run TriggerDagRun tasks in the Go runtime #74417 get merged first (their commits are cherry-picked here so this runs on its own; only the last 3 commits are new).
• Diff for early review: jason810496/airflow@843070f...feature/go-sdk/native-dag-e2e

Why

The go_sdk e2e mode only covers Python stub Dags with Go task handlers, so nothing checks that a Dag authored in Go is parsed, stored and run end to end.

What

• go-sdk/example/native/: a native Go Dag example. go_native_pipeline uses TaskFlow Inputs with task results and Literals, nested task groups with a labelled group edge, If, Switch, and the Variable, Connection and XCom clients. go_native_trigger uses TriggerDagRun, and go_native_report is declared in report.go.

  extract := dag.TaskGroup("extract")
  regions := extract.TaskGroup("regions")
  north := regions.Task(countRows, airflow.TaskSpec{TaskID: "north"}, airflow.Inputs(airflow.Literal("north"), airflow.Literal(3)))
  summed := extract.Task(summarize, airflow.Inputs(north, south))
  dag.If(anyRows, airflow.Inputs(summed)).Then(loaded).Else(empty)
  dag.Switch(p.pick, airflow.Inputs(summed)).Case(p.daily).Case(p.weekly)

• The go_sdk mode packs the native bundle into the Dags folder, so the Dag processor parses it with ExecutableCoordinator, and keeps the task handler bundle out of parsing with .airflowignore.

• test_go_sdk_native_dag.py checks the parsed Dags and their edges, the run's task states (the untaken If and Switch sides are skipped), the XComs, the Variable and Connection reads, and the per-Dag source in the Code view.

• go_native_trigger runs its TriggerDagRun task in the Go runtime (Go SDK: run TriggerDagRun tasks in the Go runtime #74417), and the test checks the triggered go_native_report run and its conf.

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Was generative AI tooling used to co-author this PR?

• Yes, with help of Claude Code Opus 5.5 following the guidelines