Workflow SDK adds idempotent starts

The Workflow SDK has introduced an enhancement to its start() function, enabling idempotent workflow initiations. This update allows for a workflow run to be admitted and a corresponding hook to be claimed within a single, atomic operation. This atomic step is designed to prevent issues arising from concurrent or repeated attempts to start the same workflow. Previously, developers would typically use a two-step process involving getHookByToken() followed by start(). This older method presented a potential vulnerability to a duplicate-start race condition, where a gap between looking up a hook and initiating the workflow could lead to unintended duplicate executions. The new atomic start() function addresses this by ensuring that any duplicate attempts to start a workflow will safely fail, maintaining the integrity of the process. Furthermore, the claimed hook becomes active immediately upon the run's admission, even before the workflow begins its execution. This early activation means that functions like resumeHook can operate effectively from the outset, and any messages or payloads received early are buffered and delivered in the correct sequence. Within the workflow itself, using createHook({ token }) with an identical token will now correctly bind to the hook that has already been claimed, streamlining the management of workflow states and messages.