On demand Queueable Job chaining and result enhancements

This release introduces:

1. New QueueableBuilder.chain() methods - chain() and chain(QueueableJob job), which allowing you to manually add jobs to an existing chain. You can now decide when to chain jobs — not just rely on the automatic chaining mechanism triggered when platform limits are hit.
2. Enhanced Results from QueueableBuilder enqueue(), chain(), and chain(QueueableJob job) now return the Queueable Chain State. Additionally, enqueue() indicates whether the action created a new chain, continued an existing chain, or scheduled an initial job.
   → Learn more here.
3. Access Queueable Chain State On-Demand
   Use Async.getCurrentQueueableChainState() to inspect the current chain — including all chained jobs, next job IDs, and chain type.