improvement(scheduler): drain in chunks instead of a single capped claim

Replaces the fixed MAX_CRON_CLAIMS (200) with a chunked drain loop:
claim WORKFLOW_CHUNK_SIZE + JOB_CHUNK_SIZE per iteration, process via
Promise.allSettled, repeat until both claim queries return empty or
MAX_TICK_DURATION_MS elapses. Throughput is no longer bounded by a
static per-tick ceiling; it scales until DB or trigger.dev is the
limit. Per-iteration chunk size still bounds row-lock set and fan-out
concurrency.

Extracts processScheduleItem and processJobItem so the loop body stays
readable. Existing claim semantics (FOR UPDATE SKIP LOCKED, lastQueuedAt
as the claim signal, staleness reclaim) are unchanged.

Author: TheodoreSpeaks