Fix message handler return type

[viktorprogger]

Q	A
Is bugfix?	✔️
New feature?	❌
Breaks BC?	❌
Fixed issues	❌

[what-the-diff[bot]]

PR Summary

• Updated AdapterInterface::subscribe() method The method now expects a function that returns a boolean value instead of void.
• Modified SynchronousAdapter::runExisting() for new return type It handles the updated return type from the callback and will keep processing messages until the handlerCallback returns false or there are no more messages.
• Queue::run() logic improvement for handling multiple messages It now processes as many items as possible in one run loop iteration but still stops when the maximum number of iterations is reached or canContinue on LoopInterface returns false. This improves efficiency without blocking other processes or threads for extended periods.

[codecov[bot]]

Codecov Report

Patch coverage: 100.00% and project coverage change: +0.04 :tada:

Comparison is base (ba32240) 82.77% compared to head (96f626f) 82.81%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #157 +/- ## ============================================ + Coverage 82.77% 82.81% +0.04% - Complexity 316 317 +1 ============================================ Files 36 36 Lines 842 844 +2 ============================================ + Hits 697 699 +2 Misses 145 145 ``` | [Impacted Files](https://codecov.io/gh/yiisoft/yii-queue/pull/157?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=yiisoft) | Coverage Δ | | |---|---|---| | [src/Adapter/SynchronousAdapter.php](https://codecov.io/gh/yiisoft/yii-queue/pull/157?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=yiisoft#diff-c3JjL0FkYXB0ZXIvU3luY2hyb25vdXNBZGFwdGVyLnBocA==) | `94.28% <100.00%> (+0.34%)` | :arrow_up: | | [src/Queue.php](https://codecov.io/gh/yiisoft/yii-queue/pull/157?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=yiisoft#diff-c3JjL1F1ZXVlLnBocA==) | `98.66% <100.00%> (ø)` | | Help us with your feedback. Take ten seconds to tell us [how you rate us](https://about.codecov.io/nps?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=yiisoft). Have a feature suggestion? [Share it here.](https://app.codecov.io/gh/feedback/?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=yiisoft)

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