[Bug] Sliding window example has a race

[antlai-temporal]

Describe the bug

As described in https://community.temporal.io/t/implement-sliding-window-batching-in-python/15959/2
the code https://github.com/temporalio/samples-python/blob/main/batch_sliding_window/sliding_window_workflow.py#L111-L120

            child_handle = await workflow.start_child_workflow(
                RecordProcessorWorkflow.run,
                record,
                id=child_id,
                id_reuse_policy=WorkflowIDReusePolicy.ALLOW_DUPLICATE,
                parent_close_policy=workflow.ParentClosePolicy.ABANDON,
            )

            self.children_started_by_this_run.append(child_handle)
            self.current_records.add(record.id)

completes the workflow task with the await, and it could happen that the started child finishes, and send a completion signal, before the record.id is added to self.current_records. Then, the signal handler will ignore
the notification...

The proposed solution is to add the record.id before starting the child workflow, as described in the link.

Minimal Reproduction

make the child workflows finish immediately without sleep...

Environment/Versions

• OS and processor: [e.g. M1 Mac, x86 Windows, Linux]
• Temporal Version: [e.g. 1.14.0?] and/or SDK version
• Are you using Docker or Kubernetes or building Temporal from source?

Additional context