This PR implements a new run TTL system and queue size limits to prevent unbounded queue growth which should help prevent situations where queues enter a "death spiral" where the queue will never be able to catch up.

The main/correct way to battle this situation is to enforce a maximum TTL on all runs (e.g. up to 14 days) where runs that have been queued for that maximum TTL will get auto-expired, making room for newer runs to execute. This required creating a new TTL system that can handle higher workloads and is now deeply integrated into the RunQueue. When runs are enqueued with a TTL, they are added to their normal queue as well as to the TTL queue. When runs are dequeued, they are removed from both their normal queue and the TTL queue. If runs are dequeued by the TTL system, they are removed from their normal queue. Both these dequeues happen automatically so there is no race condition.

The TTL expiration system is also made reliable by expiring runs via a Redis worker, which is enqueued to atomically inside the TTL dequeue lua script.

Optional associated waitpoints

Additionally, this PR implements an optimization where runs that aren't triggered with a dependent parent run will no longer create an associated waitpoint. Associated waitpoints are then lazily created if a dependent run wants to wait for the child run post-facto (via debounce or idempotency), which is a rare situation but is possible. This means fewer waitpoint creations but also fewer waitpoint completions for runs with no dependencies.

Environment Queue Limits

Prevents any single queue growing too large by enforcing queue size limits at trigger time.

• Queue size checks happen at trigger time - runs are rejected if queue would exceed limit
• Dashboard UI shows queue limits on both the Queues page and a new Limits page
• In-memory caching for queue size checks to reduce Redis load

Batch trigger fixes

Currently when a batch item cannot be created for whatever reason (e.g. queue limits) the run will never get created, which means a stalled run if using batchTriggerAndWait. We've updated the system to handle this differently: now when a batch item cannot be triggered and converted into a run, we will eventually (after retrying 8 times up to 30s) we will create a "pre-failed" run with the error details, correctly resolving the batchTriggerAndWait.