Add lease transaction statistics

[pkaminski]

Summary

• track acquired and contended task lease transactions, including NodeFire tries and duration metadata
• expose additive leaseTransactions rollups at physical source, logical queue, and global levels
• add resetLeaseTransactions() snapshot-and-reset support for interval-based StatsD and Sentry metrics
• add a per-queue captureLeaseTransactionMetrics(outcome, tries, duration) callback for acquired, contended, and failed transactions
• expose a worker-local, non-enumerable _lease.firstAcquisition flag on a task's first acquisition
• isolate metric callback failures from lease processing
• preserve the lifetime-cumulative tasksAcquired field and bump the package to 4.2.0

Motivation

Running several Firelease instances can amplify Firebase transaction load when they race to acquire the same task. These counters and the callback make that amplification measurable without changing lease behavior, while the reset API lets parent applications publish non-cumulative metrics safely. The first-acquisition flag lets parent workers distinguish newly queued work from retries without persisting instrumentation state.

Validation

• yarn test (10 tests passed)
• yarn lint
• yarn check-types
• yarn pack --dry-run
• git diff --check

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