ReentrantLock Not Properly Used in AtOnce.java Causes Potential Thread Safety Issue

[0pdd]

The puzzle 4884-97fce65f from #4884 has to be resolved:

eo/eo-runtime/src/main/java/org/eolang/AtOnce.java

Lines 15 to 18 in d7c6aea

	* @todo #4884:30min Use ReentrantLock instead of 'synchronized' in AtOnce.
	* We should use ReentrantLock instead of 'synchronized' to avoid potential
	* deadlocks when multiple AtOnce attributes are used together.
	* Moreover, 'synchronized' keyword is forbidden by qulice.

The puzzle was created by Yegor Bugayenko on 01-Mar-26.

Estimate: 30 minutes, role: DEV.

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[AlexNetTie]

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