fix: Interpolate clock stretch factor in log space - #644
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Clock stretch factors are speed multipliers, so they compose geometrically: the neutral value is 1.0, and slowing down by some amount is the reciprocal of speeding up by that same amount. Interpolate in log space so that a clock difference of zero yields exactly 1.0, and clock_stretch_max and its reciprocal are reached at +/- one tick of difference. The old linear interpolation produced a neutral factor of ~1.5 for clock_stretch_max of 2.0, desynchronizing the simulation even when clocks matched.
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Clock stretch was interpolated linearly between 1/max and max, so with a stretch max of 2.0 a zero clock difference still produced a factor of ~1.5 and the simulation ran fast even with synced clocks.
Since stretch factors are speed multipliers they compose geometrically, so this interpolates in log space instead, zero difference now gives exactly 1.0, and +/-1 tick reaches max and its reciprocal symmetrically.