perf: improve /logs concurrent access

[nicoloboschi]

Some improvements:

• instead of using an ordered dict we use a simple deque. The messages are already ordered by loguru.
• Locking is necessary for readers too since it could lead to incosistent data view and duplicate data
• /logs endpoint was returning empty with some combinations of parameters
• timestamp are now millis instead of float epoch
• keepalive is sent every 5 seconds instead of 1
• /logs always return messages sorted by time desc for consistency

[github-actions]

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_{Last Modified at 11 Jul 24 11:42 UTC}