Add Queue.workerLifetimeJitter to stagger worker shutdowns

[dereuromark]

Summary

Adds an optional Queue.workerLifetimeJitter config (seconds). Each worker picks a random offset in [0, workerLifetimeJitter] at startup and adds it to its effective workerLifetime / --max-runtime. When a fleet of workers is spawned at the same instant (ECS tasks, Kubernetes deployments, systemd unit with many instances), this prevents every worker from terminating on the same tick and producing a thundering-herd of simultaneous restarts.

Defaults to 0, so behavior is unchanged unless the option is set.

// config/app.php
$config['Queue']['workerLifetime'] = 300;
$config['Queue']['workerLifetimeJitter'] = 30; // workers now exit between 300s and 330s

Credit

Idea and original implementation by Rommel Penaflor (@xrompdev) in #475, where it was proposed against a legacy CakePHP 2.x Symphosize fork and therefore could not be merged directly. This PR is a fresh port to the modern Queue\Queue\Processor, keeping the operational intent intact.

Implementation notes

• Jitter is computed once per worker (right after $startTime = time() in Processor::run()), not re-rolled each loop iteration, so the exit time is stable per worker.
• Extracted into Processor::computeLifetimeJitterOffset() so the bounds/default behavior is unit-testable without spinning up the full run loop.
• Only applied when $maxRuntime > 0 — unlimited workers stay unlimited.
• <= 0 jitter values are ignored (returns 0), so a misconfigured negative value is a no-op rather than an error.
• If jitter was applied, the worker logs Applying worker lifetime jitter: +Ns seconds so operators can see the stagger in action.

Docs

Added a dedicated bullet in docs/sections/configuration.md directly after the workerLifetime section, explaining the ECS/K8s use case.

[codecov-commenter]

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Codecov Report

❌ Patch coverage is 80.00000% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 77.22%. Comparing base (5410512) to head (781c3c3).

Files with missing lines	Patch %	Lines
src/Queue/Processor.php	80.00%	2 Missing ⚠️
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Additional details and impacted files

@@            Coverage Diff            @@
##             master     #476   +/-   ##
=========================================
  Coverage     77.22%   77.22%           
- Complexity      949      954    +5     
=========================================
  Files            45       45           
  Lines          3196     3219   +23     
=========================================
+ Hits           2468     2486   +18     
- Misses          728      733    +5     

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