Improving performance for scheduled workflows

### Value Prop

Improved performance in how scheduled workflows are handled. Customers will experience more reliable execution of their scheduled workflows, with fewer workflows being dropped due to system load.

### Expected Outcome

Improved performance for scheduled workflows and a significant reduction in the number of workflows delayed. Customers can rely on their scheduled workflows running consistently and on time.

No files, tests, or implementation entry points are mentioned. First clarify the scheduled-workflow subsystem and how performance will be measured; done means fewer dropped or delayed workflows and more consistent on-time execution.

索引モデルが issue の本文から書いたものです。