Provide and use higher resolution padding callback timers
During testing, I noticed that the timers.c callbacks could be up to 10 milliseconds late on an otherwise idle Linux laptop tor client. They might be even later on busy relays.
Circuit fingerprinting results may be impacted by this delay. If a deep learning classifier is able to determine padding cells through recognizing this delay, padding will entirely ineffective.
It would be nice to have either high priority timers for things like this, or at least better idle resolution.
We do not yet have enough results to say with certainty if high accuracy padding timers are more important for clients, or for relays.
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