Add e2e tests for checking stub tasks against their task handlers

[jason810496]

Stack (bottom to top), on native #74037 (stack #74170): #73973, #73974, #73975, #74317, #73976, #74067, #74135, #74140, #74141, #73971, #74030, #74031, #74032, #74136, #74137, #74138, #74139

Adds end-to-end tests of #74135's check against real Go, Java and TypeScript artifacts. A Go and a Java fixture have deliberately wrong stub tasks, and the e2e tests of all three Lang-SDK modes read the Dag processor's parse logs and the REST API to see what it did.

# airflow-e2e-tests/go-test-bundle/dags/go_task_handler_failures.py
@task.stub(queue=_QUEUE)
def not_registered(): ...

@task.stub(queue=_QUEUE)
def takes_two_numbers(first: int, second: int, third: int): ...

@dag(dag_id="go_task_handler_failures")
def go_task_handler_failures():
    not_registered()
    takes_two_numbers(1, 2, 3)

Stub tasks in go_task_handler_failures.py do not match their task handlers:
- Dag 'go_task_handler_failures', task 'not_registered': 'handlers' in Dag bundle 'go-test-task-handlers' registers no task handler for it
- Dag 'go_task_handler_failures', task 'takes_two_numbers' ('handlers' in Dag bundle 'go-test-task-handlers'): passes 3 arguments, the task handler takes 2

• The Dag processor gets the worker's artifacts and runtimes in the go_sdk, java_sdk and ts_sdk compose overrides, so it can run the check.
• Native's Java and Node Dag importers register in every Dag bundle, so they would import every mounted JAR and TypeScript bundle as a Dag file, hundreds of them through the Scala example's dependency JARs. The harness writes an .airflowignore holding * into each artifact directory to keep them out. The check is unaffected, because the coordinator's scan reads the filesystem directly. A real deployment with several coordinators of one class sets [sdk] dag_bundle_to_coordinator instead.
• airflow dags reserialize is skipped in the Lang-SDK modes, so the Dag processor's own parse, with the check, is the first one. A readiness gate then waits until every Lang-SDK Dag file has a probe record and the import errors are exactly the expected ones, so no test races that parse.
• The tests check that every Lang-SDK Dag file gets a probe record, no artifact is probed twice in one parse, a later parse probes nothing new, only the fixtures fail to import, with the exact expected text, and Go's name mismatch is only a warning.
• The real-probe unit tests now run in each Lang-SDK e2e job, and in CI they fail instead of skipping when the toolchain is missing.
• The three Lang-SDK e2e jobs also run for changes to the Dag processor's task handler modules, the coordinators and the shared e2e harness. dag_processing/processor.py stays out on purpose: it is only the check's call site, its unit tests cover it, and it changes too often to trigger three compose jobs each time.

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