fix: correct mutex unlock in IsClosed.Err() method>

[honeynil]

Fixed a critical concurrency bug in the Err() method where defer was
calling RLock() instead of RUnlock(). This caused read locks to
accumulate without being released, leading to potential deadlocks when
CloseWithCause() attempted to acquire a write lock.

The bug could manifest in high-concurrency scenarios where multiple
goroutines call Err() while another attempts to call CloseWithCause().

Changes:

• trm/drivers/is_closed.go:73: Changed defer a.mu.RLock() to defer a.mu.RUnlock()

[coveralls]

Pull Request Test Coverage Report for Build 18771899929

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 94.389%

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Totals
Change from base Build 18256243043:	0.0%
Covered Lines:	1615
Relevant Lines:	1711

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💛 - Coveralls

[maranqz]

Thank you for catching and the fix. ❤️

I extended test and will release it in short time.