Logs: fix file-descriptor-sink race condition

Context

In File_descriptor_sink module, when using daily-log option, a file is created everyday to write logs on disk. There could be a race condition if two events are emitted when the rotation occurs: one will remove the file and the other try to write on it.

The issue comes from the fact that reading the current state of sinks is not part of the critical section.

Manually testing the MR

use remy@sink-race-condition-debug-fail to run a node and witness the Bad file descriptor errors occuring. use remy@sink-race-condition-debug and ensure no error of this kind occures.

Checklist

• Document the interface of any function added or modified (see the coding guidelines)
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• Provide automatic testing (see the testing guide).
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