Event timestamps needed

[tib888]

Some unit tests are randomly failing on slow or overloaded testing hardware likely due the usage of Instant::now() all over teh code. It would be better to record the press / release event timestamps at matrix scanning, and use that in tap/hold timing decisions, timeouts, etc.

If the keyboard is split, it would be nice to synch the clocks of parts, and send the scan result over the chanel together with time stamp, so the transmission delays effect would also reduce, but synching is tricky!

[HaoboGu]

iirc now the pressing time is recorded by keyboard.timer, but the releasing time is not.