Fix: CloudWatch/Watchtower logs dropped in Task SDK due to handler lifetime bugs

[korex-f]

Three related bugs all produce WatchtowerWarning: "Received message after logging system shutdown", causing CloudWatch log streams to be truncated or never created.

Bug 1 (task-sdk/src/airflow/sdk/log.py):
In configure_logging(), remote.processors was accessed before the inner configure_logging() call ran dictConfig(). dictConfig() calls _clearExistingHandlers() → logging.shutdown() on all existing handlers, killing the just-created watchtower handler (shutting_down=True) before any task log is emitted. Fix: move getattr(remote, "processors") to after dictConfig runs, injecting via a second structlog.configure() call.

Bug 2 (providers/amazon/.../cloudwatch_task_handler.py):
CloudWatchRemoteLogIO.handler was a cached_property — once killed by logging.shutdown() the dead instance was never replaced. The processors cached_property also captured _handler in a closure, pinning the dead instance. Fix: convert handler to a regular property that recreates when shutting_down=True; access self.handler dynamically in the processors closure.

Bug 3 (task-sdk/src/airflow/sdk/execution_time/supervisor.py):
_configure_logging() returned a plain tuple with no cleanup path. The only code that ever closed the remote handler was logging.shutdown() at process exit, which fired after supervise_task() returned while final task messages were still in flight. Fix: convert _configure_logging() to a contextmanager that explicitly flushes and closes the handler after process.wait() drains all task log messages.

closes: #66475